what are the best radar wavelengths incidence angles and polanzations for discrimination among lava flows and sedimentary rocks a statistical approach linear discriminant analysis of multifrequency and multipolarization radar scatterometer data of lava flows and sedimentary rocks indicates that the lava flows sampled at the snake river plain idaho and the sedimentary formations sampled at the san rafael swell utah can be discriminated from one another the necessary radar backscatter data and optimum wavelengths polarizations and incidence angles among those available for these problems are indicated by the discriminant analysis program for separation of the lava flows shorter wavelengths and smaller incidence angles are best for the sedimentary rocks conversely the longer wavelengths and somewhat larger incidence angles are preferred separation among the lava flows was slightly better using horizontally polarized data while vertical polarization gave better separation with the sedimentary rocks the method developed here may provide a rationale for user selection tion of operating parameters for advanced radar systems such as the shuttle imaging radar c sir c and that proposed for the earth observation system eos the analysis is being extended to other study sites for which we have scatterometer data to determine the generality of the results reported here

a quad pol radar scattering model for use in remote sensing of lava flow morphology abstract mapping of spatial variations in surface roughness over large regions is required to understand the nature of volcanic terrains an invertible scattering model for quad polarization radar data is presented to assist in the remote sensing analysis of lava flow surface morphology this model permits separation of the polarized part of the radar echo into quasispecular dihedral and small perturbation scattering components based on an assumed surface dielectric constant tests are presented for a quad pol scene of craters of the moon national monument in idaho where there are a number of basaltic lava flows of differing surface morphology comparison of calculated model components with the observed morphology of the lava flows suggests that this technique may be useful for the remote description of changes in surface roughness the scattering mechanisms chosen to represent the polarizing behavior of the real surface display correlations which indicate that they are sensitive to the expected scales of roughness

post impact alteration of surficial suevites in ries crater germany hydrothermal modification or weathering processes alteration of surficial suevites at ries crater germany was studied by means of x ray diffraction and scanning electron microscopy here we discuss the origin of hydrous silicate clay phases in these suevites that have been previously interpreted as resulting from post impact hydrothermal processes the results of this study indicate that the dominant alteration phases are dioctahedral al fe montmorillonite and halloysite which are typical low temperature clay minerals we suggest that the surficial suevites are not altered by hydrothermal processes and that alteration occurred by low temperature subsurface weathering processes if the surficial suevites were indeed hydrothermally modified during the early stages of post impact cooling then the alteration was of limited character and is completely masked by later weathering

magellan mission summary magellan started mapping the planet venus on september 15 1990 and after one cycle one venus day or 243 earth days had mapped 84 of the planet s surface this returned an image data volume greater than all past planetary missions combined spacecraft problems were experienced in flight changes in operational procedures and reprogramming of onboard computers minimized the amount of mapping data lost magellan data processing is the largest planetary image processing challenge to date compilation of global maps of tectonic and volcanic features as well as impact craters and related phenomena and surface processes related to wind weathering and mass wasting has begun the magellan project is now in an extended mission phase with plans for additional cycles out to 1995 the magellan project will fill in mapping gaps obtain a global gravity data set between mid september 1992 and may 1993 acquire images at different view angles and look for changes on the surface from one cycle to another caused by surface activity such as volcanism faulting or wind activity

fission track dating of haughton astrobleme and included biota devon island canada haughton astrobleme is a major extraterrestrial impact structure located on devon island in the canadian arctic archipelago northwest territories apatite grains separated from shocked precambrian gneiss contained in a polymict breccia from the center of the astrobleme yielded a fission track date of 22 4 million 1 4 million years before the present or early miocene aquitanian this provides a date for the impact event and an upper limit on the age of crater filling lake sediments and a flora and vertebrate fauna occurring in them a geologically precise date for these fossils provides an important biostratigraphic reference point for interpreting the biotic evolution of the arctic

a rough surface scattering function for titan radar studies 1 numerous studies show a relationship between radar backscattering and surface roughness while estimating the statistical properties of small scale topography is of particular interest for geologic analysis of cassini radar data there is no analytic description of radar scattering over a wide range of incidence angles and roughness this paper presents an empirical function that links the rms slope at the horizontal scale of the wavelength and hh or vv polarization radar echoes the model is based on comparison of 24 cm wavelength airsar data for lava flows in hawai i at incidence angles of 25 to 55 with topographic profiles at 25 cm posting comparison of model predictions to the range of observed titan echoes suggests that the radar return is often dominated by a component arising from subsurface scattering

composition of impact melt particles and the effects of post impact alteration in suevitic rocks at the yaxcopoil 1 drill core chicxulub crater mexico petrographical and chemical analysis of melt particles and alteration minerals of the about 100 m thick suevitic sequence at the chicxulub yax 1 drill core was performed the aim of this study is to determine the composition of the impact melt the variation between different types of melt particles and the effects of post impact hydrothermal alteration we demonstrate that the compositional variation between melt particles of the suevitic rocks is the result of both incomplete homogenization of the target lithologies during impact and subsequent post impact hydrothermal alteration most melt particles are andesitic in composition clinopyroxene rich melt particles possess lower sio2 and higher cao contents these are interpreted by mixing of melts from the silicate basement with overlying carbonate rocks multi stage post impact hydrothermal alteration involved significant mass transfer of most major elements and caused further compositional heterogeneity between melt particles following backwash of seawater into the crater palagonitization of glassy melt particles likely caused depletion of sio2 al2o3 cao na2o and enrichment of k2o and feotot during an early alteration stage since glass is very susceptible to fluid rock interaction the state of primary crystallization of the melt particles had a significant influence on the intensity of the postimpact hydrothermal mass transfer and was more pronounced in glassy melt particles than in wellcrystallized particles in contrast to other occurrences of chicxulub impactites the yax 1 suevitic rocks show strong potassium metasomatism with hydrothermal k feldspar formation and whole rock k20 enrichment especially in the lower unit of the suevitic sequence a late stage of hydrothermal alteration is characterized by precipitation of silica analcime and na bearing mg rich smectite among other minerals this indicates a general evolution from a silica undersaturated fluid at relatively high potassium activities at an early stage toward a silica oversaturated fluid at relatively high sodium activities at later stages in the course of fluid rock interaction

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

morphology stratigraphy and surface roughness properties of venusian lava flow fields 1 morphologic characteristics flow stratigraphy and radar backscatter properties of five lava flow fields on venus turgmam fluctus zipaltonal fluctus tuli mons uilata fluctus var mons and mylitta fluctus were examined to understand flow field emplacement mechanisms and relationships to other surface processes these analyses indicate that the flow fields studied developed through emplacement of numerous thin flow units presumably over extended periods of time although the venusian fields display flow morphologies similar to those observed within terrestrial flow fields the venusian flow units are significantly larger and have a larger range of radar backscatter coefficients both simple and compound flow emplacement appear to have occurred within the flow fields a potential correlation between flow rheology and radar brightness is suggested by differences in planform morphology apparent flow thickness and apparent sensitivity to topography between bright and dark flows distributary flow morphologies may result from tube fed flows and postemplacement modification by processes such as flow inflation and crustal foundering is consistent with discrete zones of increased radar brightness within individual flow lobes mapping of these flow fields does not indicate any simple evolutionary trend in eruptive resurfacing style within the flow fields or any consistent temporal sequence relative to other tectonic and volcanic features

radar backscatter from mars properties of rock strewn surfaces abstract rock strewn surfaces are apparently common on mars and radar backscatter data offer the most direct means for remotely estimating their statistical properties this paper examines the height statistics of power law and exponential rock size frequency distributions and demonstrates the dependence of root mean square rms height on horizontal scale as a function of the distribution parameters in general strewn surfaces have an inherent variation in roughness for horizontal length scales below the maximum rock diameter this leads to variations in radar echo power with wavelength even when the differential diameter function has an inverse cubed power law form size frequency data for a rock strewn test site in hawaii are consistent over a specific range of horizontal scales with a power law distribution an exponential form while better describing the rapid decline in rock abundance above a certain size threshold underestimates the population at the smaller scales most relevant to radar scattering rock sphericity statistics often cited in descriptions of rocky areas appear to be consistent with a rayleigh distribution of major and minor axis diameters about any chosen mean value depolarized backscatter data for the test site at 5 7 68 cm are proportional to the rms height at the wavelength scale mirroring a similar trend for continuous rough rocky surfaces an empirical model relating rms height to depolarized backscatter coefficient appears to well describe the behavior of strewn surfaces the polarized echoes are consistent with mie scattering from surface rocks for a reasonable choice of dielectric properties but the number of free parameters and the interaction of the scatterer and surface yields weak remote sensing roughness or dielectric constraints while depolarized backscatter data provide robust estimates of the rms height for continuous and discrete roughness populations their use in mars landing site planning is model dependent for single wavelength data we cannot uniquely determine the size frequency distribution and the maximum rock diameter dual wavelength observations in the s to p band range may better constrain the surface properties

lava flow topographic measurements for radar data interpretation surface topography is of great importance in radar backscattering but the quantitative interpretation of data collected in the field is still a difficult problem we present topographic profiles at 25 cm and 5 cm horizontal resolution for three sites along a lava flow on kilauea volcano and use these data to illustrate techniques for surface roughness analysis height and slope distributions and the height autocorrelation function are evaluated as a function of varying lowpass filter wavelength for the 25 cm data rms slopes are found to increase rapidly with decreasing topographic scale and are typically much higher than those found by modeling of magellan altimeter data for venus a more robust description of the surface roughness appears to be the ratio of rms height to surface height correlation length for all three sites this parameter falls within the range of values typically found from model fits to magellan altimeter waveforms the 5 cm profile data are used to estimate the effect of small scale roughness on quasi specular scattering

radar investigation of mars mercury and titan radar astronomy is the study of the surfaces and near surfaces of solar system objects using active transmission of modulated radio waves and the detection of the reflected energy the scientific goals of such experiments are surprisingly broad and include the study of surface slopes fault lines craters mountain ranges and other morphological structures electrical reflectivities contain information about surface densities and to some extent the chemical composition of the surface layers radar probes the subsurface layers to depths of the order of 10 wavelengths providing geological mapping and determinations of the object s spin state radar also allows one to study an object s atmosphere and ionic layers as well as those of the interplanetary medium precise measurements of the time delay to surface elements provide topographic maps and powerful information on planetary motions and tests of gravitational theories such as general relativity in this paper we limit our discussion to surface and near surface probing of mercury mars and titan and review the work of the past decade which includes fundamentally new techniques for earth based imaging the most primitive experiments involve just the measurement of the total echo power from the object the most sophisticated experiments would produce spatially resolved maps of the reflected power in all four stokes parameters historically the first experiments produced echoes from the moon during the period shortly after world war ii see e g evans 1962 but the subject did not really develop until the early 1960s when the radio equipment was sufficiently sensitive to detect echoes from venus and obtain the first doppler strip maps of that planet the first successful planetary radar systems were the continuous wave cw radar at the goldstone facility of the caltech s jet propulsion laboratory and the pulse radar at the mit lincoln laboratory all of the terrestrial planets were successfully studied during the following decade yielding the spin states of venus and mercury a precise value of the astronomical unit and a host of totally new discoveries concerning the surfaces of the terrestrial planets and the moon this work opened up at least a similar number of new questions although the early work was done at resolution scales on the order of the planetary radii very rapid increases in system sensitivities improved the resolution to the order of 100 km but always with map ambiguities recently unambiguous resolution of 100 m over nearly the entire surface of venus has been achieved from the magellan spacecraft using a side looking synthetic aperture radar reviews of the work up to the magellan era can be found in evans 1962 muhleman et al 1965 evans hagfors 1968 see chapters written by g pettengill t hagfors and j evans and ostro 1993 the radar study of venus from the magellan spacecraft was a tour de force and is well described in special issues of science volume 252 april 12 1991 and in the journal of geophysical research volume 97 august 25 and october 25 1992 venus will not be considered in this paper even though important polarization work on that planet continues at arecibo goldstone and the very large array vla in this paper we review the most recent work in earth based radar astronomy using new techniques of earth rotation super synthesis at the vla in new mexico operated by the national radio astronomy observatory and the recently developed long code techniques at the arecibo observatory in puerto rico operated by cornell university note it was recently brought to our attention that the vla software doubles the flux density of their primary calibrators consequently it is necessary to half the radar power and reflectivity numerical values in all of our published radar results from the vla goldstone radar the symbiotic relationship in these new developments for recent advances in our understanding of mercury and mars is remarkable vla imaging provides for the first time unambiguous images of an entire hemisphere of a planet and the long code technique makes it possible to map mars and mercury using the traditional range gated doppler strip mapping procedure which was apparently developed theoretically at the lincoln laboratory by paul green based on a citation in evans 1962 richard goldstein was the first to obtain range gated planetary maps of venus as reported in carpenter goldstein 1963 such a system was developed earlier for the moon as reported by pettengill 1960 and pettengill henry 1962 we first discuss the synthesis mapping technique

bulk composition of regolith fines on lunar crater floors initial investigation by lro mini rf abstract identifying polarimetric radar signatures of ice in smooth regolith fines on the floors of permanently shadowed lunar craters is hindered by uncertainties in their dielectric properties we address this deficiency through polarimetric radar analysis of surface backscatter to derive the dielectric constant e r of smooth rock free regolith fines covering brecciated crater floors observed by mini rf which offer ideal locations for unambiguous retrieval of surface e r from linear polarimetric scattering models and cpr analysis for volatile identification specifically we select fines covering crater fills in north polar and equatorial regions to constrain the range of variability of e r as a function of latitude and crater diameter where we hypothesize that the latter is indicative of the excavation depth of these fines our observations suggest that there is measurable variability in the dielectric properties of fines on lunar crater floors as a function of crater size and potentially with impact excavation depth suggesting that small craters e r ranging from 2 3 to 3 and large ones 5 km have higher values of e r that range from 3 to 3 8 we find that the most plausible explanation for the observed variability of e r of regolith fines on crater floors is mineralogical differences suggesting an increase in metal abundance in the original excavated substrate with depth i e in the uppermost kilometer of the lunar crust finally we suggest that regolith fines on the floors of permanently shadowed craters

surface modification of venus as inferred from magellan observations of plains in sedna planitia clear stratigraphic relations can be discerned among volcanic flow units young flows exhibit sar specific cross section values similar to fresh terrestrial basalt flows whereas older flows exhibit backscatter signatures similar to degraded terrestrial basalt flows total degradation of 1 m depth over 0 6 b y is inferred for the sedna area from radar signatures impact crater abundances and ejecta superposition relations with respect to volcanic flow units analyses of parabolic ejecta deposits associated with the crater stuart imply that the material is typically centimeters in thickness a relatively small fraction 10 of venusian impact craters exhibit prominent parabolic ejecta deposits these craters are interpreted to be relatively young and parabolic deposits are interpreted to be dispersed by aeolian activity over at least tens of millions of years the inferred dispersal rate 10 3 m yr is too low to produce the degradation of flows at sedna planitia and it is concluded that the dominant flow modification process is in situ weathering in addition elevation dependent weathering is inferred in western ovda regio where plains above 6054 km radius have enhanced reflection coefficients as compared to adjacent plains at lower elevations the inferred rate of generation of high reflection coefficient materials is no more than 10 2 m yr based on the inability of aeolian activity to cover high reflectivity surfaces with normal reflection coefficient materials and the ubiquitous nature of high reflectivity surfaces at high elevations surface modification rates on venus are orders of magnitude lower than on earth venusian rates are also much lower than the inferred rate of aeolian dispersal of friable materials on mars but are comparable to the estimated rate of weathering and erosion of martian bedrock low surface modification rates imply that it will be possible to determine regional scale age variations on venus based on the degree of preservation of volcanic landforms and microwave signatures

episodic river flooding events revealed by palynological assemblages in jurassic deposits of the brent group north sea spore and pollen sporomorph assemblages from middle jurassic marine deposits of the brent group in the northern north sea are investigated to assess temporal and spatial variations in vegetation and depositional processes four wells were sampled for palynology from the penguins cluster and the don north east fields through the rannoch formation shoreface succession hyperpycnite deposits occur throughout but are concentrated within the lower part of the section these are expressed by sand prone beds displaying waxing and waning current motifs normally graded muddy beds and structureless mudstones hyperpycnal hypopycnal deposits resulting from episodic river flooding represent important sedimentary features as they may be preserved below fair weather wave base in more offshore settings and potentially be the only record of the former presence of a nearby river mouth the hyperpycnites typically contain abundant botryoccocus spp amorphous organic matter aom and hinterland sporomorph taxa with relatively few marine components compared to associated marine shoreface facies variations in palynofacies assemblages and botryococcus spp abundances indicate frequent river mouth avulsion ordination of samples using non metric multidimensional scaling nmds indicates that shoreface samples of the sampled wells are relatively distinct but hyperpycnite samples are highly similar regardless of their sampled well this suggests that depositional processes and spore pollen sources i e catchment zones were similar among hyperpycnite events across different wells abundant bisaccate pollen botryococcus spp and aom within interpreted hyperpycnites suggest sediment mixing along the fluvial drainage path during flooding events the terrestrial signature of hyperpycnite sporomorph assemblages demonstrates that underflows remained coherent as they descended the shoreface profile with little turbulent mixing with ambient marine waters sporomorph assemblages display few large changes through time suggesting vegetation on the adjacent coastal plain was relatively static through the studied interval

hydrothermally altered impact melt rock and breccia contributions to the soil of mars samples of melt rock and breccia from 12 terrestrial impact craters were examined to identify alteration minerals and their conditions of formation the dominant assemblage in most cases is clay silica k feldspar zeolite indicating hydrothermal alteration at low pressures and temperatures of 100 300 c the clays are predominantly fe chlorites and smectites in most cases depleted in al and enriched in fe and mg relative to their source rocks alteration of impact glass is often complete while alteration of crystalling melt rock is limited to a few percent of the rock volume impact breccia is altered to only a small extent compared to the alteration of glass impact induced hydrothermal alteration is to be expected at martian impact sites if significant quantities of ground ice and or water are present the alteration products are likely to resemble the clays found at terrestrial craters al fe fractionation similar to that observed on earth is strongly suggested by the viking soil analyses the quantitative contribution of hydrothermal clays to the soil of mars is estimated based on a model which predicts the generation of the equivalent of a 61 m thick blanket of impact melt planet wide the inefficiency of melt production in small craters and the inefficiency of alteration in large craters limit the expected production of clay to a few percent of this figure clays produced by impact induced hydrothermal alteration may be expected to contribute to the fines on mars but this contribution is probably not dominant relative to other suggested sources

re evaluating the age of the haughton impact event we have re evaluated the published age information for the haughton impact structure which was believed to have formed 23 ma ago during the miocene age and report new ar ar laser probe data from shocked basement clasts this reveals an eocene age which is at odds with the published miocene stratigraphic apatite fission track and ar ar data we discuss our new data within this context we have found that the age of the haughton impact structure is 39 ma which has implications for both crater recolonization models and post impact hydrothermal activity future work on the relationship between flora and fauna within the crater and others at high latitude may resolve this paradox

the nature of lunar volatiles as revealed by mini rf observations of the lcross impact site 1 on 9 october 2009 the lunar crater observation and sensing satellite lcross impacted cabeus crater located near the south pole of the moon prior to that impact the mini rf instruments on isro s chandrayaan 1 and nasa s lunar reconnaissance orbiter lro obtained s band 12 6 cm synthetic aperture radar images of the impact site at 150 and 30 m resolution respectively these observations show that the floor of cabeus has a circular polarization ratio cpr comparable to or less than the average of nearby terrain in the southern lunar highlands furthermore 2 of the pixels in cabeus crater have cpr values greater than unity this observation is not consistent with the presence of thick deposits of nearly pure water ice within a few meters of the lunar surface but it does not rule out the presence of small 10 cm discrete pieces of ice mixed in with the regolith in addition mini rf on lro acquired a postimpact s band image of the region surrounding the lcross impact site providing important geologic context for the site registering the lro image to a near infrared nir image taken by the lcross shepherding spacecraft we find that the impactor landed in the ray of a fresh radar bright 1 km crater however the difference between preimpact and postimpact images is not above the speckle noise this implies that the size of the lcross impact crater is less than mini rf s resolution 30 m and or that the impact did not excavate more decimeter size blocks than were already present at the impact site

footwall uplift associated with late jurassic normal faulting in the northern north sea tilted fault blocks in the north sea show varying degrees of erosion such footwall erosion is predicted by the domino model of extension in which rigid fault blocks rotate as extension proceeds profiles of three north sea fields snorre brent and heather are analysed to estimate the amount of uplift that accompanied late jurassic normal faulting and these estimates are compared with the footwall uplift predicted by the domino model agreement between observed and predicted uplift is excellent varying from 1 km at snorre to c 100 m at heather for a given amount of extension large fault blocks tend to be bounded by large faults and to show a greater degree of erosion the brent province of the northern north sea is an area of prolific hydrocarbon discoveries almost all of the major oil fields occur in tilted fault blocks which were formed by late jurassic extension and subsequently buried by cretaceous tertiary thermal subsidence badley et al 1988 marsden et al 1990 the crests of the tilted blocks are typically eroded or degraded with varying amounts of middle lower jurassic and upper triassic section removed this footwall erosion is commonly ascribed in the literature to pre rifting doming ziegler 1982 heterogeneous stretching coward 1986 local transpression beach 1985 or even regional compression frost 1987 the purpose of this paper is to show that the uplift and degradation is a direct consequence of the late jurassic normal faulting and fault block rotation the degree of uplift is related in a simple way to the size across strike of

multipolarization radar images for geologic mapping and vegetation discrimination the nasa jpl airborne synthetic aperture radar system produces radar image data simultaneously in four linear polarizations hh vv vh hv at 24 6 cm wavelength l band with 10 m resolution across a swath width of approximately 10 km the signal data are recorded optically and digitally and annotated in each of the channels to facilitate a completely automated digital correlation both standard amplitude and also phase difference images are produced in the correlation process individual polarization and range dependent gain functions improve the effective dynamic range but as yet do not permit absolute quantitative measurements of the scattering coefficients however comparison of the relative intensities of the different polarizations in individual black and white and color composite images provides discriminatory mapping information in the death valley california area rough surfaces of young alluvial deposits produce strong responses at all polarizations smoother surfaces of older alluvial deposits show significantly lower responses evaporite deposits of different types and moisture contents have distinct polarization signatures in the wind river basin wyoming sedimentary rock units show polarization responses that relate to differences in weathering local intensity variations in like polarization images result from topographic effects strong cross polarization responses denote the effects of vegetation cover and in some cases possible scattering from the subsurface in the savannah river plant south carolina forest cover characteristics are discriminated by polarization responses that reflect the density and structure of the canopy and the presence or absence of standing water beneath the canopy

impact induced hydrothermal activity within the haughton impact structure arctic canada generation of a transient warm wet oasis field studies and analytical scanning electron microscopy indicate that a hydrothermal system was created by the interaction of water with hot impact generated rocks following formation of the 24 km diameter 23 ma haughton impact structure hydrothermal alteration is recognized in two settings within polymict impact breccias overlying the central portion of the structure and within localized pipes in impact generated concentric fault systems the intra breccia alteration comprises three varieties of cavity and fracture filling a sulfide with carbonate b sulfate and c carbonate these are accompanied by subordinate celestite barite fluorite quartz and marcasite selenite is also developed particularly in the lower levels of the impact breccia sheet the fault related hydrothermal alteration occurs in 1 7 m diameter subvertical pipes that are exposed for lengths of up 20 m the pipes are defined by a monomict quartz carbonate breccia showing pronounced fe hydroxide alteration associated sulfides include marcasite pyrite and chalcopyrite we propose three distinct stages in the evolution of the hydrothermal system 1 early stage 200 c with the precipitation of quartz vapor phase dominated 2 main stage 200 100 c with the development of a two phase vapor plus liquid zone leading to calcite celestite barite marcasite and fluorite precipitation and 3 late stage 100 c with selenite and fibroferrite development through liquid phase dominated precipitation we estimate that it took several tens of thousands of years to cool below 50 c following impact during this time haughton supported a 14 km diameter crater lake and subsurface water system providing a warmer wetter niche relative to the surrounding terrain the results reveal how understanding the internal structure of impact craters is necessary in order to determine their plumbing and cooling systems

scale dependent surface roughness behavior and its impact on empirical models for radar backscatter one goal of radar remote sensing is the extraction of terrain statistics and surface dielectric properties from backscatter data for some range of wavelengths incidence angles and polarizations this paper addresses empirical approaches used to estimate terrain properties from radar data over a wider range of roughness than permitted by analytical models many empirical models assume at least implicitly that roughness parameters like rms height or correlation length are independent of the horizontal length scale over which they are measured in contrast to recent surveys of natural terrain which show that self affine or power law scaling between horizontal scale and roughness statistics is very common the rms slope at the horizontal scale of the illuminating wavelength s lambda is directly related to the variogram or structure function of a self affine surface can be readily obtained from field measured topography and when used in an empirical model avoids the need for arbitrary wavelength dependent terms to facilitate comparison with earlier approaches an expression that links the rms height at some profile length with the rms allan deviation at an equivalent horizontal sampling interval is obtained from numerical simulations an empirical model for polarimetric scattering as a function of s lambda at 35deg 60deg incidence from smooth to rugged lava surfaces is derived and compared with earlier models for backscatter from modestly rough soil surfaces the asymptotic behavior of polarization ratios for the lava flows suggests that the depolarization of linear polarized illuminating signals occurs as a first order process likely through single scattering by rock edges or other discontinuities rather than as the solely multiple scattering effect predicted by some analytical models efforts to fully understand radar scattering from geological surfaces need to incorporate wavelength scale roughness perhaps through computational simulations

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

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

mixed hydrothermal fluids and the origin of the martian soil the martian soil consists mainly of weathered basaltic rock and a salt component enriched in volatile and mobile elements primarily sulfur chlorine sodium and potassium since the discovery of this mobile element component by the viking x ray fluorescence spectrometer volcanic aerosols have been considered a likely source for these enrichments alternative sources of the mobile element component are fluids supplied to the surface by hydrothermal processes related to impact craters and volcanism we show that a mixed hydrothermal fluid model can successfully explain the composition of the mobile element component of the soil this model is constructed using terrestrial analogs constrained by the viking and pathfinder measurements of the martian soil chemistry the potential hydrothermal fluid contributions to the soil are tightly constrained because the relative abundances of the mobile elements in hydrothermal fluids are nearly constant the two end member types of hydrothermal fluids considered in the model are the neutral chloride and the acid sulfate type the neutral chloride fluids have high cl and na contents and a significant amount of k but their s abundance relative to cl s cl ratio is too low to match the martian soil however acid sulfate hydrothermal systems characterized by substantial vapor transport and high s cl ratios are likely on mars due to the low abundance of water indeed as the availability of water declines in a hydrothermal system the neutral chloride system can evolve to a vapor dominated acid sulfate system a combination of the two types of fluids can quantitatively explain the s and cl abundance in the soil and provide reasonable abundances of other mobile elements including na k and br without predicting an excess of any element measured in the soil however the hydrothermal fluids are unlikely to be involved in the formation of the magnetic minerals in the soil because the fe contents of the fluids are too low although the acid sulfate fluids have fe concentrations a factor of 100 larger than the neutral chloride fluids the acid sulfate fluids would contribute less than 1 of the total fe in the soil the volcanic aerosol models are poorly constrained in contrast to the hydrothermal fluid models because in volcanic aerosols the relative abundances of the mobile elements are highly variable therefore while volcanic aerosols can explain the mobile element component of the soil significant contributions from other sources cannot be excluded determining the relative contributions of hydrothermal components compared to volcanic aerosols will require measurements in the martian soil of trace elements that provide signatures of the hydrothermal fluids such as high lithium contents that are associated with neutral chloride fluids

europa ganymede and callisto new radar results from arecibo and goldstone observations of the icy galilean satellites conducted during 1987 1991 with the arecibo 13 cm system and the goldstone 3 5 cm system yield significant improvements in our knowledge of the satellites radar properties hardly any wavelength dependence is seen for either the total power radar albedo or the circular polarization ratio c for europa ganymede and callisto our 13 cm estimates of mean values and rms dispersions are 1 39 0 14 and 0 69 0 06 and c 1 53 0 03 1 43 0 06 and 1 17 0 04 radar albedo features are seen on each satellite evidence for c features is lacking except for indications of a weak hemispheric asymmetry for callisto that intersatellite and intrasatellite fractional variations in albedo greatly exceed variations in c is consistent with predictions of coherent backscatter theory and implies that albedo might be a crude indicator of relative silicate abundance the satellites albedo distributions overlap the most prominent radar features are tentatively identified with galileo regio and the valhalla basin estimates of echo doppler frequencies show callisto to be lagging its ephemeris by 200 50 km

rietveld analysis of x ray powder diffraction patterns as a potential tool for the identification of impact deformed carbonate rocks previous x ray powder diffraction xrd studies revealed that shock deformed carbonates and quartz have broader xrd patterns than those of unshocked samples entire xrd patterns single peak profiles and rietveld refined parameters of carbonate samples from the sierra madera impact crater west texas unshocked equivalent samples from 95 miles north of the crater and the mission canyon formation of southwest montana and western wyoming were used to evaluate the use of x ray powder diffraction as a potential tool for distinguishing impact deformed rocks from unshocked and tectonically deformed rocks at sierra madera dolostone and limestone samples were collected from the crater rim lower shock intensity and the central uplift higher shock intensity unshocked equivalent dolostone samples were collected from well cores drilled outside of the impact crater carbonate rocks of the mission canyon formation were sampled along a transect across the tectonic front of the sevier and laramide orogenic belts whereas calcite subjected to significant shock intensities at the sierra madera impact crater can be differentiated from tectonically deformed calcite from the mission canyon formation using rietveld refined peak profiles weakly shocked calcite from the crater rim appears to be indistinguishable from the tectonically deformed calcite in contrast rietveld analysis readily distinguishes shocked sierra madera dolomite from unshocked equivalent dolostone samples from outside the crater and tectonically deformed mission canyon formation dolomite

magellan observations of extended impact crater related features on the surface of venus a total of 57 parabolic shaped and 9 approximately circular extended impact crater related features have been found in magellan synthetic aperture radar sar and thermal emissivity data covering 92 of the surface of venus the parabolic features are with seven exceptions oriented e w with the apex to the east and the impact crater located just west of the apex they were first identified in the surface emissivity data derived from magellan radiometry measurements but the great majority are only clearly visible in the sar imagery the overall sizes of both the parabolic and circular features range from several hundred to about two thousand kilometers and are loosely correlated with the diameters of the parent craters the floors of almost all these craters have high specific radar backscatter cross sections i e they are bright in the sar imagery relative to their surroundings and tend to have low emissivities approximately one third of the impact craters with diameters 15 km appear to have bright floors and about half of these have an associated parabolic feature which can be observed in the sar or emissivity data no features have been found which overlie the parabolic features indicating that they are among the youngest features on the surface of the planet this suggests that radar bright floors characterize the freshest impact craters and that modification processes subsequently darken their radar signature a model for the formation of the parabolic features is developed based on the injection of small particles into the upper atmosphere at the time of impact and their transport to the west by the e w zonal winds fitting of a small perturbation scattering model to the measured average scattering law for the parabolic features placed an upper limit of about 0 6 cm on the wavelength scale 12 6 cm surface roughness and hence of 1 to 2 cm on the largest particle sizes of interest fallout times from 50 km in the venus atmosphere for particles of this size are about 2 hours allowing westerly drifts of several hundred kilometers for zonal winds of 50 to 100 m s 1 measurements of the change in backscatter cross section of features overlaid by these extended ejecta deposits are consistent with deposit depths of a few centimeters to 1 or 2m

fluidization and hydrothermal alteration of the suevite deposit at the ries crater west germany and implications for mars the formation cooling and alteration of the impact ejecta deposits at the ries crater are an analog for impact processes and the formation of regoliths and soils on mars we have studied the suevite deposit an impact melt bearing breccia found outside of the crater rim this suevite contains large numbers of chimney like degassing pipes apparently formed by high gas pressures in the hot 500 c fluidized suevite immediately after deposition of the suevite the likely sources of the gas are volatiles from the melted and shocked basement inclusions the suevite outside of the crater rim contains about 15 wt clay indicating a large amount of alteration of the suevite the clay is an fe rich montmorillonite with less than 5 interstratified illite indicating that the temperature at which most of the alteration occurred was less than 100 130 c the duration of this low temperature period may have been extended by additional heating from the exothermal alteration reactions the surfaces of the degassing pipes are not altered to clays however but have a thin fe rich oxide or hydroxide coating the absence of alteration in the pipes suggests that the main alteration event outside the crater occurred under unsaturated conditions such that the walls of the pipes were dry suevite deposits are likely to exist on mars because of the presence of volatile rich target rock martian suevites may have also been fluidized and hydrothermally altered contributing significantly to the formation of the clay like phases inferred to exist in the martian soil

inference of surface power spectra from inversion of multifrequency polarimetric radar data during the summer of 1988 an intensive field experiment was conducted in the vicinity of pisgah lava field in the mojave desert of southern california as part of the experiment physical properties such as microtopography composition soil moisture and dielectric constant at five different sites representing surfaces with r m s heights varying from less than one centimeter to tens of centimeters were measured in addition polarimetric radar images at p band 68 cm wavelength l band 24 cm and c band 5 7 cm were acquired at three different incidence angles with the nasa jpl airborne imaging radar polarimeter using trihedral corner reflectors deployed in the area prior to imaging the radar images were calibrated to provide 0 values for each resolution element in each scene this paper reports on the derivation of the power spectrum of surface microtopography by solution of the small perturbation model for multiple incidence angle and multiple frequency radar data power law fits to the power spectra have exponents slope in log log plots that are nearly the same for all surfaces these values are close to those from measured microtopography profiles the offset in log log plots shows very good correlation with measured power spectrum offsets however the image derived offsets are consistently lower than measured values this may be the result of calibration errors using the wrong dielectric constants in the inversion or the fact that not all observed energy was scattered by the surface interface alone

mobile element analysis by secondary ion mass spectrometry sims of impactite matrix samples from the yaxcopoil 1 drill core in the chicxulub impact structure the concentrations of the fluid mobile trace elements lithium beryllium boron and barium were measured in samples of the altered matrix of several impactite breccias of the yaxcopoil 1 drill core using secondary ion mass spectrometry sims to determine the extent of transport due to aqueous or hydrothermal processes three of the elements li be and b have higher concentrations in the upper suevite impact breccias than in the lower impact melt deposits by factors of 3 5 2 2 and 1 5 respectively lithium and b are the most enriched elements up section and appear to have had the greatest mobility the similar fractionation of li and b is consistent with fluid transport and alteration under low temperature conditions of less than 150 c based on published experimental studies in contrast to li be and b the concentration of ba in the altered matrix materials decreases upward in the section and the concentration of ba in the matrix is an order of magnitude less than the bulk concentrations likely due to the presence of barite the origin of the elemental variations with depth may be related to different protolith compositions in the upper versus the lower impactite units a different protolith in the altered matrix is suggested by the mg rich composition of the lower units versus the al rich composition of the upper units which largely correlates with the mobile element variations the possibility that vertical transport of mobile elements is due to a postimpact hydrothermal system is supported by published data showing that the sediments immediately overlying the impactites are enriched in mobile elements derived from a hydrothermal system however the mobile elements in the sediments do not have to originate from the underlying impactites in conclusion our data suggests that the impactites at this location did not experience extensive high temperature hydrothermal processing and that only limited transport of some elements including li be and b occurred

surface morphology of domes in the marius hills and mons rumker regions of the moon from earth based radar data 1 clusters and coalesced complexes of domes represent a relatively rare landform within the extensive low relief lunar maria while they are typically spectroscopically similar to mare basalts emplaced by high volume low viscosity eruptions the large scale morphology of the domes is more consistent with slower emplacement and or more viscous magma we use new earth based radar data to study the decimeter to meter scale rock abundance at the surface and buried within the probing range of the radar signal of domes in the marius hills and mons rumker regions domes of the marius hills are characterized by high circular polarization ratio cpr values at 12 6 cm and 70 cm wavelength similar to the near rim ejecta deposits of young lunar craters like tycho areas of large ejecta fragments near the rim of meteor crater and blocky lavas such as sp flow in arizona we infer that a very rugged flow surface morphology associated with the original dome forming eruption rather than postemplacement modification exists beneath at most a few meters of regolith magmas with greater silica content than sampled lunar basalts are unlikely so the blocky structure of the dome forming lava must arise from some combination of compositional change effusion rate and or cooling effects not typically observed in basaltic landforms on the earth much of the 80 km diameter mons rumker has low backscatter and cpr at 12 6 cm wavelength relative to nearby mare terrain at 70 cm wavelength the northern and most of the southern parts of the complex are radar dark but there is a radar bright feature that extends from the central region eastward into oceanus procellarum we conclude that much of mons rumker is mantled by rock poor fine grained pyroclastic material the radar bright feature in the 70 cm map is detectable owing to some combination of greater roughness like the marius domes and thinner mantling cover

development of rift basins illustrated by the structural evolution of the oseberg feature block 30 6 offshore norway the mesozoic tilted fault block in norwegian north sea block 30 6 containing the giant oseberg oil and gas field is used to illustrate basin development during the jurassic and cretaceous there is seismic evidence for an early rifting phase in the northern viking graben on which the jurassic cretaceous rifting phase early bathonian to berriasian is overprinted the oseberg structure is representative of other fault blocks bordering the northern viking graben axis planar normal faults and listric faults which were restricted to the rifting phase dominate both fault types exhibit syn fault sedimentation listric faulting is recognized on seismic sections by the differential tilting reverse drag antithetic faulting and a wedge shaped syn rift reflector package the initiation of rifting is dated by baselap onto pre rift reflectors and cessation is dated by an unconformity beneath the generally onlapping post rift sediments steeply dipping planar normal faults often active along previously established fault zones played a significant part in the post rift development of the basin the last movement on planar normal faults in the oseberg fault scarp becomes younger away from the rift axis and this produced the complex fault scarp visible on many seismic lines the topography defined by the post rift unconformity is a composite surface which formed in response to subsidence processes it is not the result of orogenic events such as the kimmerian 9orogeny9 footwall uplift associated with planar normal faults caused local unconformities in complex fault scarps and on fault block crests

unsupervised classification of scattering behavior using radar polarimetry data the use of an imaging radar polarimeter data for unsupervised classification of scattering behavior is described by comparing the polarization properties of each pixel in an image to that of simple classes of scattering such as even number of reflections odd number of reflections and diffuse scattering for example when this algorithm is applied to data acquired over the san francisco bay area in california it classifies scattering by the ocean as being similar to that predicted by the class of odd number of reflections scattering by the urban area as being similar to that predicted by the class of even number of reflections and scattering by the golden gate park as being similar to that predicted by the diffuse scattering class it also classifies the scattering by a lighthouse in the ocean and boats on the ocean surface as being similar to that predicted by the even number of reflections class making it easy to identify these objects against the background of the surrounding ocean

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

volatile transport on venus and implications for surface geochemistry and geology the high vapor pressure of volatile metal halides and chalcogenides e g of cu zn sn pb as sb bi at typical venus surface temperatures coupled with the altitude dependent temperature gradient of 8 5 k km 1 is calculated to transport volatile metal vapors to the highlands of venus where condensation and accumulation will occur the predicted geochemistry of volatile metals on venus is supported by observations of cu zn sn pb as sb and bi minerals around terrestrial volcanic vents spectroscopic observations of cucl in volcanic gases at kilauea and nyiragongo and large enrichments of these and other volatile elements in terrestrial volcanic aerosols a one dimensional finite difference vapor transport model shows the diffusive migration of a thickness of 0 01 to 10 m yr of moderately to highly volatile phases e g metal halides and chalcogenides from the hot lowlands 740 k to the cold highlands 660 k on venus the diffusive transport of volatile phases on venus may explain the observed low emissivity of the venusian highlands hazes at 6 km altitude observed by two pioneer venus entry probes and the pioneer venus entry probe anomalies at 12 5 km

tb or not tb banding in turbidite sandstones recognition and interpretation of sedimentary structures is fundamental to understanding sedimentary processes banded sandstones are an enigmatic sedimentary facies comprising alternating mud rich as matrix and or mud clasts and cleaner sand layers the juxtaposition of hydrodynamically different grain sizes contradicts established models of cleaner sand bedform development here outcrop subsurface core and petrographic data from three deep water systems with well constrained paleogeographic contexts are used to describe the range of sedimentary textures bedform morphologies and facies associations and to quantify the mud content of banding banding can occur in any part of a bed base middle or top but it typically overlies a structureless basal sandstone or mud clast conglomerate lag and is overlain by clean parallel laminated sandstone and or ripple cross lamination banding morphology ranges from sub parallel to bedforms that comprise low angle laminae with discontinuous lenses of mudstone or asymmetric bedforms comprising steeply dipping foresets that transition downstream into low amplitude bedwaves or steeply dipping ripple like bedforms with heterolithic foresets this style of banding is interpreted as a range of bedforms that form progressively in the upper stage plane bed flow regime via tractional reworking beneath mud laden transitional plug flows the balance of cohesive and turbulent forces and the rate of flow deceleration aggradation rate govern the style of deposit banded sandstones and linked debrites are rarely found juxtaposed together in the same bed because they are distributed preferentially in proximal and distal settings respectively understanding the origins of banding in turbidite sandstones the conditions under which it forms and its distribution across deep water systems and relationship to linked debrites is important for it to be used effectively as a tool to interpret the geological record

a study of p band synthetic aperture radar applicability and performance for mars exploration imaging subsurface geology and detecting shallow moisture 1 over the past decade orbital images of the martian surface revealed key evidence about the history of the planet environment craters faults paleo lakes and rivers partially hidden under a widespread layer of aeolian deposits furthermore several recent observations and studies support the hypothesis that water could be found in the shallow subsurface of mars low frequency synthetic aperture radar sar has demonstrated its subsurface imaging capabilities on earth especially in arid regions while sar potentials for mars exploration have already been widely discussed we present here results of a theoretical and parametric study based on the experience we gained from terrestrial surveys on mars analog test sites which evaluates the capabilities of a p band 430 mhz sar for mars exploration for both shallow subsurface geology mapping and moisture detection we suggest that a p band polarimetric sar can probe the first meters of the martian subsurface to reveal the dust covered geology and to monitor moisture changes over large scales

the unique radar properties of silicic lava domes 1 silicic lava domes exhibit distinct morphologic characteristics at scales of centimeters to kilometers multiparameter radar observations capture the unique geometric signatures of silicic domes in a set of radar scattering properties that are unlike any other natural geologic surfaces backscatter cross section values are among the highest observed on terrestrial lava flows and show only a weak decrease with incidence angle cross polarization backscatter hv shows a unique behavior increasing with increasing wavelength circular polarization ratios are relatively high in the 0 3 0 95 range and increase with increasing wavelength field measurements of boulder size frequency distributions and microtopography indicate that silicic dome surfaces are among the roughest ever measured rms heights at a 1 m lateral scale range from 13 cm to 50 cm rms slopes at 1 m spacing range from 12 to 43 degrees modeling of the scattering behavior suggests it results from a combination of rough surface facet scattering and scattering from block edges that act as a random collection of dipoles the unusual wavelength dependence of the radar parameters appears to result from a higher component of edge scattering at large wavelengths producing for example higher cross polarized backscatter at p band 68 cm steep sided volcanic domes on venus superficially resemble terrestrial silicic domes in plan view gross morphology but few similarities remain when the radar scattering and three dimensional shapes of the features are compared the unique radar scattering properties suggest that such volcanic surfaces can be identified with multiparameter radar observations in future planetary radar missions and in active terrestrial volcanoes where dome development can represent serious hazards

regolith properties in the south polar region of the moon from 70 cm radar polarimetry abstract the south polar region of the moon contains areas permanently shadowed from solar illumination which may provide cold traps for volatiles such as water ice previous radar studies have emphasized the search for diagnostic polarization signatures of thick ice in areas close to the pole but near surface regolith properties and regional geology are also important to upcoming orbital studies of the shadowed terrain to study regional regolith variations we collected 70 cm wavelength 450 m resolution dual circular polarization radar data for latitudes 60 90 s using the arecibo and greenbank telescopes the circular polarization ratio c is sensitive to differences in rock abundance at the surface and up to tens of m below the surface depending upon the regolith loss tangent we observe significant variations in c attributed to changes in the surface and subsurface rock population across the south polar highlands concentric haloes of low polarization ratio surrounding hausen moretus and other young craters represent rock poor ejecta layers values of c up to 1 occur in the floors and near rim deposits of eratosthenian and copernican craters consistent with abundant rocky ejecta and or fractured impact melt enhanced c values also correspond to areas mapped as orientale derived plains forming material wilhelms d e howard k a wilshire h g 1979 usgs map i 1162 and similar polarization properties characterize the permanently shadowed floors of craters faustini and shoemaker small areas of very high 1 5 circular polarization ratio occur on shadowed and seasonally sunlit terrain and appear to be associated with small craters we suggest that regolith in low lying areas near the south pole is characterized by a significant impact melt component from orientale which provides a source for excavation of the block rich ejecta around small craters observed in this and earlier radar studies the lower portion of the interior wall of shackleton crater permanently shadowed from the sun but visible from earth is not significantly different in 70 cm scattering properties from diurnally seasonally sunlit areas of craters with similar morphology

lava flow surface roughness and depolarized radar scattering surface roughness has a strong controlling influence on radar scattering and other types of remote sensing observations we compare field measurements of surface topography and dielectric constant for a range of lava flow textures to aircraft multipolarization radar observations at 5 7 24 and 68 cm c l and p band wavelengths the roughness is found to vary with scale in a self affine fractal manner for scale lengths between 25 cm the smallest horizontal step size and 3 5 m this result is used to demonstrate that a two component surface description consisting of the fractal dimension and rms height or slope at some reference scale can resolve some of the ambiguities in previous efforts to quantify roughness at all three radar wavelengths the hv backscatter cross section is found to vary in an approximately exponential fashion with the rms height or allan deviation at some reference scale up to a saturation point where the surface appears entirely diffusely scattering to the radar based on these observations we use a parameter defined as the ratio of rms height to the particular scale of measurement backscatter values at 24 cm wavelength and the topographic profile data were used to derive expressions which link the hv radar cross section to or to the analogous wavelength scale rms slope these equations provide a reasonable fit to 24 and 68 cm echoes and for rough surfaces at 5 7 cm but yield poor results for 5 7 cm echoes on smooth terrain we conclude that the roughness at the two larger scales is well described by a single fractal dimension and rms height but that texture at very small scales is characterized by different statistics this inference is supported by analysis of 5 cm horizontal spacing topographic profiles the relationships defined here allow determination of the surface rms height or slope at the scale of the radar wavelength given radar data at additional wavelengths a more complete view of the statistical properties of the surface can be developed such techniques may be useful in analyses of synthetic aperture radar images for terrestrial volcanic areas magellan data for venus and other planetary radar observations

preliminary observations of volcanoes with the sir c radar the two flights of the shuttle imaging radar sir c x sar in april and october 1994 provided a wealth of new image data over many of the world s volcanoes including 13 of the 15 international decade volcanoes a first look at these data shows that mapping of remote volcanoes e g nyiragongo and nyamuragira in africa will now be easier especially when aided by the collection of multi parameter radar data over better known analogous volcanoes such as kilauea hi the utility of the radar to identify different types of lava flows is shown for fernandina volcano galapagos islands growth of mudflow deposits lahars that were emplaced on mount pinatubo philippines during the six months between the two missions is also illustrated additionally interferometric radar data were collected over several active volcanoes the potential uses of these data for topographic mapping and ground deformation studies are discussed

geologic analyses of shuttle imaging radar sir b data of kilauea volcano hawaii analyses of imaging radar data of volcanic terranes on earth and venus have emphasized the need for a clearer understanding of how these data can be most effectively used to accomplish important volcanological goals including the interpretation of eruptive styles and the characterization of the geologic history of volcanic centers the second shuttle imaging radar experiment sir b obtained two digital images over the summit caldera and the southwest rift zone of kilauea volcano in 1984 our geologic analyses of these images indicate that sir b data are particularly useful for delineating the distribution and surface textural variations of a9a lava flows for mapping large scale topographic features with radar facing slopes and for identifying an areally extensive pyroclastic deposit analyses of the sir b data of kilauea however do not permit unambiguous identification of landforms such as pahoehoe lava flows cinder cones and fissures although separation of low return units such as pahoehoe lava flows and adjacent pyroclastic ash is not greatly improved using standard image enhancement techniques the texture analysis technique applied here did facilitate discrimination of such smooth surfaced volcanic deposits although analyses of the sir b data permit a generally accurate interpretation of the eruptive history of kilauea the inability to distinguish low return pahoehoe flows results in misinterpretation of several aspects of kilauea volcanism suggesting that caution should be exercised in the interpretation of sar data of volcanic terranes

hyperspectral mapping of alteration assemblages within a hydrothermal vug at the haughton impact structure canada meteorite impacts on earth and mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization we investigate a calcite marcasite bearing vug at the 23 km diameter haughton impact structure devon island nunavut canada using imaging spectroscopy of the outcrop in the field 0 65 1 1 m and samples in the laboratory 0 4 2 5 m point spectroscopy 0 35 2 5 m major element chemistry and x ray diffraction analyses the mineral assemblages mapped at the outcrop include marcasite marcasite with minor gypsum and jarosite fibroferrite and copiapite with minor gypsum and melanterite gypsum fe3 oxides and jarosite and calcite gypsum clay microcline and quartz hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases marcasite formed from the postimpact hydrothermal system under reducing conditions while subsequent weathering oxidized the marcasite at low temperatures and water rock ratios the acidic fluids resulting from the oxidation collected on flat lying portions of the outcrop precipitating fibroferrite copiapite that assemblage then likely dissolved and the changing chemistry and ph resulting from interaction with the calcite rich host rock formed gypsum bearing red coatings these results have implications for understanding water rock interactions and habitabilities at this site and on mars

radar polarization properties of volcanic and playa surfaces applications to terrestrial remote sensing and venus data interpretation the radar polarization properties of lava flows in hawaii kilauea and arizona sp flow and two play a surfaces lunar lake nevada and lavic lake california are compared to the predicted behaviors of theoretical scattering models at 5 7 cm and 24 cm wavelengths kilauea lava flows can be modeled by a combination of facet and diffuse dipole like scattering scattering by rock faces on the scale of the radar wavelength is proposed to account for much of the facet return the radar echoes at 24 cm wavelength from sp flow are on average consistent with entirely diffuse scattering but there are regions within the flow where circular polarization ratios exceed unity suggesting a coherent scattering effect 68 cm data for the lava flows show evidence of radar penetration and volume scattering the playa surfaces are characterized by polarization properties which in some cases are qualitatively consistent with the first order small perturbation model but the echoes do not closely match the predictions of this model for any reasonable dielectric constant value these results show that it may be difficult to construct invertible models for the polarization behavior of some surfaces the playas whereas for others the kilauea lava flows the scattering properties can be successfully modeled the first order small perturbation model is not appropriate for inverse modeling of most terrestrial lava flows though very smooth surfaces on venus may be amenable to the use of this model high circular polarization ratios observed for sp flow tentatively attributed here to coherent backscatter may be analogous to arecibo observations of high reflectivity areas on venus

the effect of interbedding on shale reservoir properties north sea oil is overwhelmingly generated in shales of the upper jurassic basal cretaceous kimmeridge clay formation once generated the oil is expelled and ultimately migrates to accumulate in sandstone or carbonate reservoirs the source rock shales however still contain the portion of the oil that was not expelled as a consequence such shales and juxtaposed non source lithofacies can form the targets for the exploration of unconventional oil in this paper we examine part of the kimmeridge clay formation as a hybrid shale resource system within which hot shale and organic lean sandstone and siltstone intervals are intimately interbedded this hybrid system can contain a greater volume of oil because of the increased storage capacity due to larger matrix porosities of the sand silt interbeds together with a lower adsorptive affinity in the interbedded sandstone the relationship between the estimated volume percentages of sand and mudstone and free oil determined from rock eval s1 yields is used to place limits on the drainage of oil from source mudstone to reservoir sand at the decimeter scale these data are used to determine oil saturations in interbedded sand mudstone sequences at peak oil maturity higher values of free hydrocarbon as evidenced by the s1 value in mudstone suggest that more oil is being retained in the mudstone while higher s1 values in the interbedded sands suggest the oil is being drained to saturate the larger pore spaces high silica content in the interbeds confirms the brittleness in this mudstone sandstone lithofacies an important factor to be considered for fracture stimulation to successfully work in a hybrid system the key points of this hybrid unconventional system are the thickness storage capacity and the possibility to capture a portion of the expelled as well as retained oil

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

compositional heterogeneity of impact melt rocks at the haughton impact structure canada implications for planetary processes and remote sensing connecting the surface expression of impact crater related lithologies to planetary or regional subsurface compositions requires an understanding of material transport during crater formation here we use imaging spectroscopy of 6 clast rich impact melt rock outcrops within the well preserved 23 5 ma 23 km diameter haughton impact structure canada to determine melt rock composition and spatial heterogeneity we compare results from outcrop to outcrop using clasts groundmass and integrated clast groundmass compositions as tracers of transport during crater fill melt rock formation and cooling supporting laboratory imaging spectroscopy analyses of 91 melt bearing breccia and clast samples and microscopic x ray fluorescence elemental mapping of cut samples paired with spectroscopy of identical surfaces validate outcrop scale lithological determinations results show different clast rich impact melt rock compositions at three sites kilometers apart and an inverse correlation between silica rich sandstone gneiss and phyllosilicate rich shales and gypsum rich rocks that suggests differences in source depth with location in the target stratigraphy gypsum is primarily sourced from 1 km depth while gneiss is from 1 8 km depth sandstone from 1 3 km and shales from 1 6 1 7 km observed heterogeneities likely result from different excavation depths coupled with rapid quenching of the melt due to high content of cool clasts results provide quantitative constraints for numerical models of impact structure formation and give new details on melt rock heterogeneity important in interpreting mission data and planning sample return of impactites particularly for bodies with impacts into sedimentary and volatile bearing targets e g mars and ceres

evaluation of an empirical radar backscatter model for predicting backscatter characteristics of geologic units at pisgah volcanic field california comparison of radar backscatter coefficients in db calculated by using the empirical model of oh et al 1992 to extracted from airsar data of four geologic units at pisgah shows that the model predicts measured vv and hv to within 3 db the model predicts higher hh than those observed for smooth surfaces rms height s s 30 the model will require modification to include surfaces with non unity hh vv

backscatter model for the unusual radar properties of the greenland ice sheet a number of planetary objects exhibit large radar reflectivity and polarization ratios and more recently a similar behavior has been observed over a vast portion of the earth s surface the percolation facies of the greenland ice sheet surface based ranging radar data and snow stratigraphy studies demonstrated that the radar properties of that portion of greenland are caused by enhanced scattering from massive large solid ice bodies buried in the top few meters of the dry cold clean snowy surface of the ice sheet and created by seasonal melting and refreezing events from author

mars orbital synthetic aperture radar obtaining geologic information from radar polarimetry 1 radar penetration of mantling layers and scattering from buried objects or interfaces is a topic of current interest in both terrestrial and planetary remote sensing we examine the behavior of surface and subsurface scattering interfaces and the types of information that may be obtained from observations in different polarizations and wavelengths these results are applied to the design of a future mars orbital synthetic aperture radar sar for which we draw the following conclusions 1 mapping of buried geologic features is best accomplished using vv polarization at an optimal wavelength determined by the competing effects of antenna gain attenuation in the dust and the reduction in effective surface roughness with wavelength p band frequencies 1 ghz or less offer the best opportunity for detection of moderately rough buried features 2 the relative roles of surface and subsurface scattering may be determined using measurements in hh and vv polarization with a channel gain calibration better than 0 5 db 3 the thickness of a mantling layer or ice mass cannot be directly inferred from multiwavelength observations layer thickness may be inferred from the interferometric correlation of backscatter measurements collected on suitably spaced orbital passes though the required phase measurement accuracy is challenging while additional information may be gained by collecting scattering data in more polarizations or wavelengths we suggest that the primary science goals of a mars orbiting radar could be accomplished by a single wavelength system capable of collecting vv and hh polarizations with the calibration and orbit control needed to permit interferometric analysis

the structural evolution of the northern viking graben and its bearing upon extensional modes of basin formation recent advances in the understanding of rift basin formation coupled with the increasing public availability of seismic and well data across the northern viking graben 60 61 n have enabled a detailed analysis of its development two rifting episodes can be recognized late permian early triassic and bathonian ryazanian major regional unconformities thought to be primarily tectonic rather than eustatic in origin separate and subdivide the rifting episodes the earlier episode involved extension about a n s axis ensuing triassic mid jurassic thermal subsidence was accommodated on steep faults during the later episode a new ne sw fault trend was superimposed on pre existing patterns major block rotation marking active rifting ceased at the end of the ryazanian during the second post rift episode there was a progressive migration of active faulting towards the basin margins and as a result a widening with time of the area undergoing subsidence asymmetric subsidence of the central part of the basin was hinged at the western margin of the horda platform and accommodated to the nw on major faults within the tampen spur factors for the second rifting episode were calculated both by relating subsidence to extension and by measuring observed extension values calculated by both methods increase consistently towards the basin axis for both rifting and thermal subsidence phases but are greater for the latter phase subsidence patterns are similar for both rifting and thermal subsidence episodes so that there is vertical stacking of relatively thick sequences in the axis of the northern viking graben these factors preclude the application of models involving uniform and non uniform stretching and also preclude oblique extension depth dependent stretching is preferred

control of impact crater fracture systems on subsurface hydrology ground subsidence and collapse mars 1 noachian layered materials are pervasively exposed throughout the highlands of mars the layered deposits in places many kilometers thick exhibit impact craters of diverse morphologic characteristics ranging from highly degraded to pristine most of which formed during the period of heavy bombardment in addition exhumed impact craters ancient channels and fluvial and alluvial fans are visible in the layered deposits through moc imagery these features are more abundant in noachian terrains which indicates relatively high erosion rates during ancient mars that competed with heavy meteoritic bombardment the noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation here we propose that impact craters buried and exposed and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic driven hydrothermal activity in and surrounding the tharsis region for example the formation of chaotic terrains the source regions of the circum chryse outflow channel system and a large diversity of collapse structures including impact crater moats and pit chains appear to be the result of enhanced hydrothermal activity

lava flow characterization at pisgah volcanic field california with multiparameter imaging radar multi incidence angle in the 25 to 55 range radar data acquired by the nasa jpl airborne synthetic aperture radar airsar at three wavelengths simultaneously and displayed at three polarizations are examined for their utility in characterizing lava flows at pisgah volcanic field california pisgah lava flows were erupted in three phases flow textures consist of hummocky pahoehoe smooth pahoehoe and aa with and without thin sedimentary cover of the eight airsar images used here four were calibrated to within an accuracy of 2 db with trihedral corner reflectors and data from these calibrations were used to process the additional images to a conservatively estimated 5 db level of accuracy calibrated radar backscatter data in db were plotted as a function of incidence angle at three wavelengths p band 68 cm l band 24 cm and c band 5 6 cm and three polarizations hh horizontal transmit horizontal receive hv horizontal transmit vertical receive and vv vertical transmit vertical receive for eight major units at pisgah for which multi incidence angle airsar data were available the eight units consist of near vent and distal aa flows near vent and distal hummocky pahoehoe flows a mantled hummocky pahoehoe flow a platform pahoehoe flow an alluvial fan and a playa analyses of these backscatter data show that major unmodified volcanic units at pisgah are readily distinguishable from each other and that they exhibit diffuse hh vv and or multiple hv scattering behavior typical of rough surfaces at these wavelengths these analyses show that discrimination of smooth lavas platform pahoehoe from mantled units with greater primary roughness hummocky pahoehoe is difficult and must rely on supporting observations such as evidence of localized weathering and or sediment deposition contrast with surrounding units and superposition of flow units l band backscatter and image data at hv polarization show the best discrimination of pisgah lava flows with optimal unit separation observed between 40 and 50 incidence angles backscatter data shown as a function of relative age of pisgah flows indicate that dating of lava flows on the basis of average radar backscatter may yield ambiguous results if primary flow textures and modification processes are not well understood

radar mapping of lunar cryptomaria east of orientale basin 1 lunar cryptomare deposits represent early basaltic volcanic material that has been mantled by or incorporated into highland rich ejecta from basin or crater forming impacts mapping these buried basalts is important for understanding regional stratigraphy and the history and extent of lunar volcanism we use new 70 cm wavelength radar images collected using arecibo observatory and the green bank telescope and clementine data to study cryptomaria east of orientale basin earlier multispectral analyses showed that mare material is mixed with the highland terrain along the western margin of oceanus procellarum leading to a detectable increase in the feo and tio2 abundance of the regolith surface the highland margin of western procellarum is also characterized by low 70 cm radar returns consistent with an increased regolith loss tangent due to ilmenite in the mare derived material the low 70 cm radar echo however persists well to the west of the mixed zone evident in multispectral data and includes the region surrounding cruger crater it is likely that mare basalt or a mixed zone of mare and highland material exists at depth across the region and only reaches the visible surface near the western procellarum margin the plausible depth to this mixed zone is dependent upon the loss tangent of the overlying pure highland ejecta if orientale ejecta is primarily low loss anorthosite then the mixed zone could lie at depths of up to several tens of meters we propose that pre orientale mare deposits flooded the region between cruger grimaldi and oceanus procellarum and also patches west and northwest of humorum basin the total area of these deposits represents 178 103 km2 or an additional 0 5 of the lunar surface covered by mare basalts

no evidence for thick deposits of ice at the lunar south pole the rim of the shackleton crater at the lunar south pole is a candidate crash site for nasa s lcross probe lunar crater observation and sensing satellite due to launch in 2008 the plume of debris kicked up by the crash is to be analysed in the hope that it will reveal the water thought to be there suggestions of lunar ice date from 1996 when data from the clementine spacecraft gave some indications of the presence of ice on crater walls at the south pole now using high resolution radar imagery the radar scattering parameter thought indicative of thick ice deposits has been found also to match radar echoes from the rock strewn walls and ejecta of young impact craters at all lunar latitudes there is no evidence for thick ice though there could be grains of water ice spread more thinly through the lunar soil shackleton crater at the moon s south pole has been suggested as a possible site of concentrated deposits of water ice on the basis of modelling of bi static radar polarization properties and interpretations of earlier earth based radar images1 2 this suggestion and parallel assumptions about other topographic cold traps is a significant element in planning for future lunar landings hydrogen enhancements have been identified in the polar regions3 but these data do not identify the host species or its local distribution the earlier earth based radar data lack the resolution and coverage for detailed studies of the relationship between radar scattering properties cold traps in permanently shadowed areas and local terrain features such as the walls and ejecta of small craters here we present new 20 m resolution 13 cm wavelength radar images that show no evidence for concentrated deposits of water ice in shackleton crater or elsewhere at the south pole the polarization properties normally associated with reflections from icy surfaces in the solar system4 5 6 were found at all the observed latitudes and are strongly correlated with the rock strewn walls and ejecta of young craters including the inner wall of shackleton there is no correlation between the polarization properties and the degree of solar illumination if the hydrogen enhancement observed by the lunar prospector orbiter3 indicates the presence of water ice then our data are consistent with the ice being present only as disseminated grains in the lunar regolith

impact crater lakes on mars the robotic search for life on mars centers on identifying accessible environments where the biological catalyst water has existed the formation of large impact craters on mars 65 km diameter may have resulted in the creation of ice covered impact crater lakes which would not freeze for thousands of years even under present climatic conditions water could be supplied from deep confined aquifers penetrated by the impact craters without the need for surface melt water freezing of the lakes is postponed owing to heat from impact generated melt bearing deposits from impact related uplift of hotter rocks from depth and from the latent heat of freezing of a deep crater lake abundant morphologic evidence for ancient crater lakes has not been found in viking images except for craters associated with outflow channels however ice covered crater lakes could have formed and further searches for evidence of these lakes are warranted the lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from mars

the radar scattering characteristics of venus landforms nine geologic units are identified in a recently published arecibo image of the venus equatorial region campbell et al 199o a detailed examination of the radar scattering properties of these units using data from the imaging mode of the pioneer venus radar mapper pvm shows them to fall into three distinct classes 1 dark plains 2 tessera narrow spaced parallel lineaments and bright and dark banded terrain and 3 bright plains mottled plains ovoids lineament belts and edifices additional units interpreted to be analogous to those mapped from the arecibo data are identified in the region imaged exclusively by pvm and are found to have similar scattering properties an examination of the scattering properties of units mapped as tessera tellus regio and eastern beta regio as compared with the northern flanks of thetis regio leads to the conclusion that part of thetis possesses characteristics similar to tellus

venus topography and kilometer scale slopes during the first 8 months of the magellan mission the radar altimeter has made some three million measurements of the surface of venus covering the latitude range from 85 n to 80 s methods involving range correlation doppler filtering multi burst summation and range migration are used to focus the observations and to achieve high surface resolution results are presented as maps of the global distribution of topography meter scale roughness and power reflection coefficient the results are similar to those reported in previous experiments surface heights exhibit a unimodal distribution with more than 80 of the surface lying within 1 km of the 6051 84 km mean radius but the higher resolution of the magellan altimeter has disclosed several surprisingly steep features e g the southwest face of the maxwell montes the southern face of the danu montes and the chasmata to the east of thetis regio where average kilometer scale slopes of greater than 30 are not uncommon this conclusion is corroborated by close inspection of synthetic aperture radar imagery

reservoir quality in the jurassic sandstone reservoirs located in the central graben north sea abstract this study investigates the diagenesis and reservoir quality of upper jurassic sandstones of ula formation from the central graben petrophysical and petrographical studies have been done on cored interval from well 2 1 6 of ula field precipitation of quartz cement is the main porosity destroying process in deeply buried quartz rich sandstone reservoirs of the north sea quartz cement precipitates in the form of syntaxial overgrowth over detrital grain of quartz grain coatings like micro quartz and illite are the main reasons for preservation of porosity in sandstones as they cover the grain and inhibit the quartz overgrowth petrographical data in this study clearly indicates that grain coatings are present in the studied samples micro quartz grain coating is the most common grain coat in the upper jurassic sandstones of ula which is generated from the transformation of siliceous sponge spicules known as rhaxella perforata clay grain coats like illite and chlorite are also present relation between intergranular volume igv versus matrix and quartz cementation versus porosity have also been studied igv is strongly affected by mechanical compaction grain size grain shape quartz and carbonate cements sandstones with high amount of matrix and fine grains have high igv as compared to coarse grains because coarse grains are compacted more when they are subjected to mechanical compaction grain shape also has a pronounced effect on porosity angular grains tend to lose porosity easier as they are subjected to stress

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

surface processes in the venus highlands results from analysis of magellan and arecibo data the highlands of venus are characterized by an altitude dependent change in radar backscatter and microwave emissivity likely produced by surface atmosphere weathering reactions we analyzed magellan and arecibo data for these regions to study the roughness of the surface lower radar backscatter areas at the highest elevations and possible causes for areas of anomalous behavior in maxwell montes arecibo data show that circular and linear radar polarization ratios rise with decreasing emissivity and increasing fresnel reflectivity supporting the hypothesis that surface scattering dominates the return from the highlands the maximum values of these polarization ratios are consistent with a significant component of multiple bounce scattering we calibrated the arecibo backscatter values using areas of overlap with magellan coverage and found that the echo at high incidence angles up to 70 from the highlands is lower than expected for a predominantly diffuse scattering regime this behavior may be due to geometric effects in multiple scattering from surface rocks but further modeling is required areas of lower radar backscatter above an upper critical elevation are found to be generally consistent across the equatorial highlands with the shift in microwave properties occurring over as little as 500 m of elevation these surfaces are not simply characterized however by the absence of a highly reflective component surface morphology and radar scattering properties suggest that a mantling deposit forms at the highest elevations most likely by in situ erosion of the original rock in ovda regio this process mantles or has removed surface festoon structure at the 1 to 10 m scale implying a significant depth for the weathered layer similar radar dark areas occur in maxwell montes but are apparently unrelated to the current topography of the region possible reasons for these observations include mass wasting from areas of steep slopes compositional or age differences within the montes vertical tectonic shifts of relict contacts local topographic effects on surface temperature or errors in the magellan topography data in the rugged terrain while there is evidence for some of these effects in the existing data no single model at present appears to satisfy all occurrences of high altitude radar dark terrain new measurements of the surface and lower atmosphere chemistry of venus are needed to further refine these conclusions

characterization of lava flow degradation in the pisgah and cima volcanic fields california using landsat thematic mapper and airsar data digital landsat thematic mapper tm observations multi frequency polarimetric airsar radar data microtopographic profiles derived from helicopter borne photography and field measurements were analyzed over the pisgah and cima volcanic fields and lavic lake playa mojave desert california surface radiance factors were extracted from tm data using radiative transfer procedures to model the atmosphere and surface simultaneously airsar data were calibrated to backscatter specific cross sections using corner reflectors deployed at a number of locations analyses focused on the use of key field sites to understand compositional and textural controls on tm band 5 1 55 to 1 75 m radiance factors and c 5 6 cm l 24 cm and p 68 cm band specific cross sections for the pisgah and lavic lake sites the tm data are explained using a linear mixing model of basalt and fine grained sediment clay to sand sized grains of clay minerals quartz feldspar carbonate and lithic fragments radiance factors with the addition of shadows for the rough a9a flow on the other hand airsar data are shown to be primarily controlled by surface roughness as there is a strong correlation between specific cross section and surface height standard deviation for the elongate flows at the cima volcanic field which exhibit a mix of pahoehoe and a9a properties we find a positive linear relationship between tm band 5 radiance factors and flow ages for the 3 m y age range represented specific cross sections remain constant until about 0 14 ma and then decrease with age up to about 0 56 ma on the other hand data for the two older flows 0 70 and 0 85 ma show increasing specific cross sections with increasing age we interpret the increase in tm band 5 radiance factors from 0 05 to 0 25 with increasing flow age and the decrease in specific cross sections 8 db change at 35 incidence angle for l band for flows up to 0 56 ma in age as due to smoothing by mass wasting and infill by fine grained aeolian deposits the increased specific cross sections for older flows are interpreted to be a consequence of surface roughness generated by fluvial dissection

dating of a regional hydrothermal system induced by the 1850 ma sudbury impact event new u pb geochronologic data from the sudbury structure directly link extensive hydrothermal activity in crater fill breccias with the 1850 ma impact event and constrain complex impact induced processes to 4 m y semiconformable alteration of breccias in the onaping formation includes silicification albitization chloritization calcitization and complex feldspathization which directly underlies zn cu pb ore deposits geochronologic data demonstrate a middle to lower crustal source for the crater fill deposit that was subsequently affected by the hydrothermal event at 1848 4 3 8 1 8 ma these and other data confirm that the crater fill breccia hydrothermal system sudbury igneous complex and its sublayer ni ore bearing units were emplaced as a result of impact the ages of events associated with the sudbury structure are now more closely constrained than in any other meteorite impact structure

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

marcasite inversion and the petrographic determination of pyrite ancestry pyrite formed by the inversion of marcasite or by oxidative leaching of pyrrhotite can be recognized in polished sections by the following characteristics compiled from synthetic pyrite after marcasite and natural samples of pyrite after marcasite and after pyrrhotite pyrite formed by inversion from marcasite is characterized by approximately 2 modal percent pore space no by products filling the pores optical anisotropy dark green to dark red anhedral shape and polycrystalline daughter pyrite domains in two orientations relative to the marcasite parent crystal pyrite or marcasite formed by oxidative dissolution as opposed to leaching of pyrrhotite exhibits up to 32 modal percent pore space gaps between the pyrite and parent pyrrhotite pores and gaps filled with by product siderite magnetite hisingerite or other fe bearing phase optically isotropic character for pyrite development of crystal faces and random orientation relative to the parent pyrrhotite marcasite formed by oxidative leaching of fe as opposed to complete dissolution from pyrrhotite also exhibits a large amount of pore space but has preferred orientation relative to the parent pyrrhotite pyrite after marcasite may be used as an indicator of ph 5 and t ca 240 degrees c during deposition of the parent marcasite marcasite precipitated following dissolution of pyrrhotite is also indicative of those conditions during alteration marcasite formed by oxidative leaching of pyrrhotite cannot be used as evidence of those conditions however

terrestrial analogues for lunar impact melt flows abstract lunar impact melt deposits have unique physical properties they have among the highest observed radar returns at s band 12 6 cm wavelength implying that they are rough at the decimeter scale however they are also observed in high resolution optical imagery to be quite smooth at the meter scale these characteristics distinguish them from well studied terrestrial analogues such as hawaiian p hoehoe and a lava flows the morphology of impact melt deposits can be related to their emplacement conditions so understanding the origin of these unique surface properties will help to inform us as to the circumstances under which they were formed in this work we seek to find a terrestrial analogue for well preserved lunar impact melt flows by examining fresh lava flows on earth we compare the radar return and high resolution topographic variations of impact melt flows to terrestrial lava flows with a range of surface textures the lava flows examined in this work range from smooth hawaiian p hoehoe to transitional basaltic flows at craters of the moon cotm national monument and preserve in idaho to rubbly and spiny p hoehoe like flows at the recent eruption at holuhraun in iceland the physical properties of lunar impact melt flows appear to differ from those of all the terrestrial lava flows studied in this work this may be due to a differences in post emplacement modification processes or b fundamental differences in the surface texture of the melt flows due to the melts unique emplacement and or cooling environment information about the surface properties of lunar impact melt deposits will be critical for future landed missions that wish to sample these materials

arecibo radar mapping of the lunar poles a search for ice deposits the arecibo 12 6 centimeter wavelength radar system was used to image the polar regions of the moon at a resolution of 125 meters in a search for ice deposits in areas of possible permanent shadow from the sun no areas greater than 1 square kilometer were found with high radar backscatter cross sections and high circular polarization ratios properties suggestive of the presence of ice a number of areas smaller than 1 square kilometer were found with these properties but optical images from spacecraft missions have shown some of these features to be in sunlight arecibo radar images of sinus iridum at latitude 47 n also showed a number of small features with similar properties the coincidence of some of these features with the radar facing slopes of craters and their presence in sunlit areas suggests that very rough surfaces rather than ice deposits are responsible for their unusual radar properties

structural analysis of the smeaheia fault block a potential co2 storage site northern horda platform north sea abstract smeaheia a prominent fault block located on the horda platform northern north sea is identified as a potential subsurface co2 storage site we utilise the gn1101 3d seismic survey to generate a high resolution subsurface geomodel to inform the structural style and evolution of the fault block to investigate geological controls on proposed co2 storage and provide a geometric framework as a basis for future analyses two basement involved first order north south trending fault systems the vette fault zone vfz and the oygarden fault complex ofc bound the 15 km wide fault block the vfz bifurcates down section where it is hard linked with two separate basement structures a phenomenon we term as dual rooted apart from activity during the permo triassic rift phase 1 and the late jurassic early cretaceous rift phase 2 we present evidence that rifting in this part of the north sea continued into the late cretaceous with minor reactivation in the palaeocene eocene two segments of the vfz interacted and linked at a relay ramp during rift phase 2 second order thin skinned faults show basement affinity and developed during rift phase 2 in two distinct pulses a population of polygonal faults intersects the overburden and developed during the eocene to middle miocene we have revised the areal extent of two structural closures that define the smeaheia fault block alpha vfz footwall and beta ofc hanging wall which consist of upper jurassic viking group target formations simplified cross fault juxtaposition analysis of the vfz and second order intra block faults are presented and inform pressure communication pathways between the smeaheia and tusse fault block as well as reservoir integrity and compartmentalisation the geomodel further identifies important geological controls on co2 storage in the fault block including a thinning caprock above the alpha structure and identification of hard linkage between deep tectonic faults and shallow polygonal faults

ground penetrating radar as a tool for probing the shallow subsurface of mars 1 design and testing of an impulse ground penetrating radar gpr for possible rover deployment on mars in 2009 is well underway the gpr has mass power volume and data rate targets of 0 5 kg 3 w peak 3400 cm3 and 0 3 mb d and will possess easily modified bistatic high frequency e g 500 600 mhz and monostatic rat tail e g 100 mhz antennas the gpr should be capable of measuring in situ radar properties on mars to depths of up to 10 20 m thereby helping to constrain near surface geology and structure initial gpr tests at the site of the 2001 fido rover field trials near cronese lake california confirm the value of the instrument in defining local geologic setting and in providing context for data collected using other rover science payload elements a rover deployed gpr may enable three dimensional mapping of local stratigraphy which in turn can assist in evaluating the history of aqueous activity and the accessibility of near surface water