buried topography of utopia mars persistence of a giant impact depression knobs partially buried craters ring fractures and some mesas permit a qualitative determination of the topography buried beneath younger northern plains materials these features are widely distributed in the utopia area but are absent in a large roughly circular region centered at about 48 degree n 240 degree w this implies the existence of a circular depression about 3 300 km in diameter buried beneath utopia planitia that is here interpreted to represent the central part of a very large impact basin the presence of buried curved massifs around part of this depression and a roughly coincident mascon lend further support present topography areal geology and paleotopography of buried surfaces all point to the persistence of this major depression for almost the entire history of mars

the global martian volcanic evolutionary history abstract viking mission image data revealed the total spatial extent of preserved volcanic surface on mars one of the dominating surface expressions is olympus mons and the surrounding volcanic province tharsis earlier studies of the global volcanic sequence of events based on stratigraphic relationships and crater count statistics were limited to the image resolution of the viking orbiter camera here a global investigation based on high resolution image data gathered by the high resolution stereo camera hrsc during the first years of mars express orbiting around mars is presented additionally mars orbiter camera moc and thermal emission imaging system themis images were used for more detailed and complementary information the results reveal global volcanism during the noachian period 3 7 ga followed by more focused vent volcanism in three tharsis elysium and circum hellas and later two tharsis and elysium volcanic provinces finally the volcanic activity became localized to the tharsis region about 1 6 ga ago where volcanism was active until very recently 200 100 ma these age results were expected from radiometric dating of martian meteorites but now verified for extended geological units mainly found in the tharsis montes surroundings showing prolonged volcanism for more than 3 5 billions years the volcanic activity on mars appears episodic but decaying in intensity and localizing in space the spatial and temporal extent of martian volcanism based on crater count statistics now provides a much better database for modelling the thermodynamic evolution of mars

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

identifying sediment sources in a gullied catchment using natural and anthropogenic radioactivity the ratio of the lithogenic nuclides 226ra and 232th indicates that the major source of sediment in transport in a gullied catchment located in the head waters of whiteheads creek new south wales australia is the gully itself this observation is supported by 7be and 137cs concentrations which indicate that the sediment is derived from erosion of either gully floor or gully wall material while subcatchment 7be and 137cs data show sheet rill and gully erosion are occurring in the upstream catchments sediment from these sources is either being trapped before entering the gully or the volume of sediment is small compared to that derived from the gully itself the differences in the 226ra to 232th ratio between the suspended solids collected on the rising stage and samples of sediment deposited during the falling stage at the outlet of the catchment indicate a change in the source of sediment during storm events the results presented here demonstrate the applicability of radionuclide tracers in providing quantitative estimates of the relative contributions of individual catchments to the sediment moving within a drainage network and in determining whether or not the sediments are mainly derived from subsoil or topsoil sources

steep sided domes on venus characteristics geologic setting and eruption conditions from magellan data a survey of more than 95 percent of the venus surface reveals 145 steep sided domes which can be subdivided into a variety of morphologic forms the most common being shaped like inverted bowls or flat topped domes results of a preliminary analysis of the distribution and geologic setting of the domes are presented the relation of the domes to analogous terrestrial features is examined and possible models for their mode of emplacement are outlined

lineated valley fill lvf and lobate debris aprons lda in the deuteronilus mensae northern dichotomy boundary region mars constraints on the extent age and episodicity of amazonian glacial events abstract in order to assess the nature degradational processes and history of the dichotomy boundary on mars we conducted a detailed morphological analysis of a 70 000 km 2 region of its northern portion north central deuteronilus mensae south of lyot in the vicinity of sinton crater this region is characterized by the distinctive sinuous 2 km high plateau scarp boundary outlying massifs to the north and extensive fretted valleys dissecting the plateau to the south these features represent the first order modification and retreat of the dichotomy boundary and are further modified by processes that form lineated valley fill lvf in the fretted valleys and lobate debris aprons lda along the dichotomy scarp and surrounding the outlying massifs we use new high resolution image and topography data to examine the nature and origin of lvf and lda and to investigate the climatic and accompanying degradational history of the escarpment on the basis of our analysis we conclude that 1 lvf and lda deposits within the study region are comprised of the same material show integrated flow patterns and originate as debris covered valley glaciers a significant amount of ice hundreds of meters is likely to remain today beneath a thin cover of sublimation till 2 there is depositional evidence to suggest glacial highstands at least 800 m above the present level implying previous conditions in which the distribution of ice was much more widespread this is supported by similar deposits within many other areas across the dichotomy boundary 3 the timing of the most recent large scale activity of the lda lvf in this area is about 100 500 million years ago similar to ages reported elsewhere along the dichotomy boundary 4 there is evidence for a secondary but significantly limited phase of glaciation the deposits of which are limited to the vicinity of the alcoves similar later phases have also been reported elsewhere along the dichotomy boundary 5 modification of the fretted valleys of the dichotomy boundary has been substantial locally but we find no evidence that the amazonian glacial epochs caused retreat of the dichotomy boundary of the scale of tens to hundreds of kilometers our findings support the results of an analysis just to the east of the study region and of studies carried out elsewhere along the dichotomy boundary that find further evidence for the remnants of debris covered glaciers and extensive valley glacial land systems

a novel method for determining residence times of river and lake sediments based on disequilibrium in the thorium decay series sediment fluxes in rivers have proved difficult to measure or model at timescales relevant to land and water resource management decisions determining transport rates and residence times is complicated by the intermittent movement and temporary storage of sediments in natural streams this paper presents a new tool for estimating the residence times of river borne sediments based on the observed disequilibria between the naturally occurring radionuclides 228ra and 232th in the thorium decay series disequilibrium between concentrations of 228ra half life 5 75 years and its long lived parent 232th has been observed in marine environments and in terrestrial freshwaters but has not been previously reported in fluvial sediments or soils here we report 228ra excesses in sandy stream and silty lake sediments from southeastern australia the excess is developed in hillslope soils in the catchment headwaters and begins to decay back to secular equilibrium once the sediment is finally removed from contact with the soil water the short half life of 228ra enables this process to be used to investigate fluvial sediment transfers and alluvial and lacustrine sediment storages over the past 30 years when combined with indicators of sediment source such as 226ra 232th and 230th 232th ratios observation of this excess should provide a useful new tool for examining the residence and transit times of bed load and suspended load sediments in streams and lakes

lead 210 sediment geochronology in a changing coastal environment abstract sediment accumulation rate studies utilizing excess 210 pb and 137 cs were conducted as part of recent investigations of biogeochemical cycling at a single site in cape lookout bight a rapidly changing coastal basin on the outer banks of north carolina u s a cores three meters in length reveal a depositional history for the bight interior characterized by a gradual transition in texture from coarse grained to fine grained material over the period 1946 1979 this transition is controlled by progressive enclosure of the bight by an active northerly migrating recurved spit the textural gradation is periodically interrupted by layers of well sorted sand associated with major storm events lead 210 data indicate that the upper meter of the sediment has accumulated at a rate of 3 35 to 4 71 g cm 2 yr 1 or approximately 8 4 to 11 8 cm yr 1 at o 0 84 below 120 cm depth dilution of clay and silt by low activity sand necessitates correction of the 210 pb profile in order to establish a geochronology grain size 210 pb distribution measurements at three depths reveal that the specific activity dpm g 1 of clay is 3 2 times that of silt and 24 7 times that of sand corrections of bulk sediment excess 210 pb activities based on these measurements lead to dates for textural changes which are consistent with charted changes in basin morphology and major storm events sixteen 137 cs measurements between 33 241 cm depth reveal a peak activity at 105 115 cm and indicate a minimum sedimentation rate of approximately 2 7 g cm 2 yr 1

a 120 year record of changes in nitrogen and carbon cycling in lake alexandrina south australia c n δ15n and δ13c in sediments variations in 15n and 13c and c n ratios of organic matter in sediment cores in lake alexandrina south australia show that there have been modifications of n and c sources due to land use changes water diversions and irrigation since european settlement of the surrounding basin in the middle 1800s 15norg and 13corg concentrations from three short sediment cores range from 1 8 to 3 9 and 26 7 to 21 1 respectively all cores showed a 2 increase in 15n over the top 100 mm with little variation below about 150 mm 13c values increased by about 3 from the base of the sediment cores to a maximum of 21 at 150 mm depth before decreasing by 5 to 27 over the top 100 mm c n mass ratios 11 suggest that organic matter preserved in the sediment is composed primarily of aquatic plant material with terrestrial plants contributing 10 excess 210pb and 137cs dating indicate a sediment accumulation rate of 3 1 mm a 1 suggesting the enrichment in 15n began in the 1950s and the 13c maxima corresponds to approximately 1940 the increase in 15n concentration over the past 30 50 a is attributed to the increasing agricultural expansion and development in the lower catchment particularly intensive grazing of cattle for dairying the authors suggest that there has been an increased flux of 15n enriched inorganic n derived from mineralized animal waste and sewage to the river and lake over the past 30 40 a which in turn is incorporated into the aquatic plants the variation in 13c reflects a change from terrestrial dominated input of inorganic c to increasingly marine dominated sources after water diversions commenced in the late 1800s once barrages were completed at the outlet of the lake in 1939 to prevent seawater intrusion the aquatic plants in the lake reverted to assimilation of dissolved inorganic c derived from oxidation of terrestrial organic matter

the 210pb chronology of late holocene deposition in an eastern australian lake basin we report here the results of detailed 210pb analysis of a sequence of lake sediments from little llangothlin lagoon on the new england tablelands of new south wales australia 210pb dating has been rarely employed in australia and prior to this work no attempt had been made to evaluate the method using independent dating techniques the chronology of deposition in the lake has been modelled using the constant initial concentration cic and constant rate of supply crs methods changes in the palynology and geochemistry of the sediments can be closely matched with well documented historic events in the lake catchment the dates of these events have been used to assess the modelled chronologies within the limits of resolution of the sampling interval there is good agreement between the chronology modelled using the crs approach and the dates inferred for geochemical and palynological events in the sequence the cic method provides a less successful match with the historical record although the differences between the dates derived by the two models are small

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

topography within circular grabens implications for polygon origin utopia planitia mars 1 very large fracture bounded polygons occur in acidalia and utopia planitiae mars two models for the origin of these large polygons postulate drape folding of a sedimentary cover material over an uneven buried surface with the strain enhancement needed to explain the large size due to differential compaction throughout the polygonal terrain are circular grabens inferred to overlie buried crater rims drape folding models predict that 1 these circular grabens will bound topographic lows and 2 the surface relief and percent compaction within circular grabens will be proportional to ring diameters relief and compaction within 8 circular grabens have been determined by gridding mola data in arcview all 8 fulfill the first prediction and 7 of them fulfill the second prediction these results support a sedimentary origin for polygonal terrain materials and thus are consistent with the past existence of an ocean in the martian lowland

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

global and regional ridge patterns on mars abstract over 16 000 wrinkle ridges on mars have been classified mapped and digitized to provide a large computer accessible data base for analyzing regions subjected to possible compressive stresses the survey has revealed major compressive structures that occur well beyond the tharsis dominated hemisphere the large variety of affected geologic terrains indicate stresses not simply localized in the intercrater plains one major area of inferred compression occurs in the southern cratered highlands near longitude 180 w where major ridges and scarps extend over 3000 km the occurrence and orientation of many ridges are locally controlled by ancient impact basins the chryse basin in particular has an important effect on ridges in northern lunae planum the removal of all basin concentric ridges reveals however a complex global pattern although such patterns may yet be controlled by heavily degraded impact basins major regional trends also emerge that appear to require broader scale global stresses most ridges in the western hemisphere are shown to be orthogonal to three centers corresponding to tharsis 1 n 122 w syria 12 s 104 w and chryse 19 n 47 w ridges not included in these three sets are generally more random and highly localized most but by no means all ridges in the eastern hemisphere are controlled by the hellas and isidis basins a simple global grid is not yet identifiable and may not be recognizable owing to the large number of regional patterns

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

glacially influenced sedimentation in the later proterozoic of the paraguay belt mato grosso brazil abstract late proterozoic probably early vendian 610 590 ma glaciogenic and turbiditic sediments and metasediments are present along the transitional zone between the amazonian craton to the northwest and the paraguay belt to the southeast in the cuiaba region mato grosso brazil a few exposures of diamictites are associated with conglomerates and graded pebbly sandstones on the cratonic fringe and pass southeastwards into fine grained sediments deposited in the deeper part of the probably marine basin in the paraguay belt these rocks have been affected by the brasiliano orogeny possibly around 570 ma they show increasing deformation and metamorphism from the craton towards the fold belt the sedimentation scheme proposed for the western border of the paraguay belt and the eastern edge of the amazonian craton involves three probably marine main depositional systems to the west on the craton the platform domain can be subdivided into a western inner shelf and an eastern outer shelf the deposits on the inner shelf subdomain show an alternation of dominant massive diamictites sandstones and fine grained sediments with few dropstones this diamictite association is tentatively interpreted as glaciomarine in origin in the outer shelf subdomain the massive diamictites are progressively replaced southeastwards by an association of massive diamictites stratified diamictites and fine grained sediments this diamictite association is interpreted as a whole as resedimented glacial debris deposited by subaqueous debris flows the slope domain located at the transition between craton and fold belt is characterized by strong reworking of the glaciomarine sediments by gravity flows responsible for a type of submarine fan deposition the coarse clastic facies which result from a reworking by rapid downslope transport of cohesive debris flows and gravity flows with high viscosity fill feeder channels in the upper fan eastward inside the belt a progressive sorting in the deeper portions of the fan is shown by the transition from diamictites massive gravels sandstone intercalations with occasional inverse and or normal grading debris flow turbidity current to normal graded finer sediments turbidity current sandstone and siltstone intercalations represent interchannel deposits formed by turbidity currents east of the slope well bedded fine grained sediments were generated by low density turbidity currents direct glacial influence is reduced to the presence of a few isolated clasts or dropstones two distinct upper proterozoic glaciogenic units are known in brazil the older and more widespread one dated at about 950 ma is located on the sao francisco craton and in the adjacent brasiliano fold belts the younger one 600 ma is restricted to the paraguay belt and the adjacent border of the amazonian craton in southern western gondwana late proterozoic glaciation is of mountain type and developed at latitudes of 60 on highs probably generated by pan african brasiliano rifting at the same time in its northern part a widespread ice sheet covered the west african craton

martian rampart crater ejecta experiments and analysis of melt water interaction abstract viking images of martian craters with rampart bordered ejecta deposits reveal distinct impact ejecta morphology when compared to that associated with similar sized craters on the moon and mercury topographic control of distribution lobate and terraced margins cross cutting relationships and multiple stratigraphic units are evidence for ejecta emplacement by surface flowage it is suggested that target water explosively vaporized during impact alters initial ballistic trajectories of ejecta and produces surging flow emplacement the dispersal of particulates during a series of controlled steam explosions generated by interaction of a thermite melt with water has been experimentally modeled preliminary results indicate that the mass ratio of water to melt and confining pressure control the degree of melt fragmentation ejecta particle size and the energy and mode of melt ejecta dispersal study of terrestrial lobate volcanic ejecta produced by steam blast explosions reveals that particle size and vapor to clast volume ratio are primary parameters characterizing the emplacement mechanism and deposit morphology martian crater ramparts are formed when ejecta surges lose fluidizing vapors and transported particles are deposited en masse this deposition results from flow yield strength increasing above shear stress due to interparticle friction

the recent history of erosion and sedimentation on the southern tablelands of southeastern australia sediment flux dominated by channel incision abstract as in other regions colonised from europe within the last few centuries australia s vegetation and soils have been dramatically changed by clearing cropping and grazing in southeastern australia particularly on the southern tablelands the impacts of european settlement are clearly manifested by channel incision by using stratigraphic and documentary evidence in conjunction with aerial photographs sediment budgets for the post settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km2 catchment of jerrabomberra creek near canberra using these budgets and some plausible assumptions it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment while the quantities estimated in this analysis are approximations the trends through time are credible sediment yield increased rapidly to a peak after european settlement and has returned to a level between the peak and the pre european value the delivery ratio has followed a similar trend the most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion this result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes the soil conservation implication of these results is clear to control off site effects of erosion the focus must be on the channels

the global distribution of wrinkle ridges on venus abstract new digital mapping of over 65 000 wrinkle ridges of the plains of venus shows a strong correlation between the location and orientation of these long low amplitude compressive anticlines and major features of the geoid and long wavelength topography regions with wrinkle ridges occupy 43 of the plains and are strongly skewed toward low elevations and negative geoid anomalies about 93 of the wrinkle ridge plains lie below mean planetary radius and 72 have negative geoid anomalies in contrast the extensional rift zones of venus are strongly skewed toward high elevations and positive geoid anomalies thus compressive deformation dominates the topographic and geoid lows whereas extensional rifting is generally restricted to the highs these observations are consistent with geoid based stress models that predict compression in geoid lows and extension in geoid highs the orientations of wrinkle ridges are generally consistent over regions extending for 1000 10 000 km many regions have multiple sets of wrinkle ridges of different orientations reflecting multiple episodes and directions of compression however about 80 of the regions display a single dominant wrinkle ridge orientation with secondary orientations subordinate the dominant wrinkle ridge orientations in many regions follow the contours of long wavelength topography and geoid or lie along the axes of troughs in the geoid thus the maximum horizontal compression recorded by the folds is commonly parallel to the present day gradient in geoid and topography although some regions are strong exceptions perhaps reflecting changes in topography and geoid with time the dominant wrinkle ridge trends ring several major geoid and topographic swells especially western aphrodite terra and lada terra with ring diameters of 75 120 8000 13 000 km in addition there are smaller rings of wrinkle ridges around the swells in themis eistla and bell regiones especially gula mons with ring diameters of 25 45 2500 5000 km in contrast there are no rings of compressive deformation surrounding some other geoid topographic highs including beta and atla regiones which have been proposed to be the youngest swells and display the largest peak geoid topography ratios and largest geoid gradients these observations are consistent with the idea that not all the major topographic geoid swells existed on venus at the time of wrinkle ridge formation

transport mechanism for pb 210 cs 137 and pu fallout radionuclides through fluvial marine systems abstract pb 210 cs 137 and pu 239 240 sediment depth profiles in an anoxic unbioturbated estuarine depositional regime at the head of the saguenay fjord que exhibit a seasonally modulated component caused by pulsed inputs of silts and sands during high energy spring river discharge events superimposed on an ambient depositional pattern of finer grained clays and organic matter a precise sediment timestratigraphy has been determined by the inverse correlation of the pb 210 activity with the rate of river discharge during the period 1963 1976 the historical record of cs 137 and pu 239 240 sediment fluxes has been reconstructed through the normalization of fallout radionuclide activities to the excess pb 210 activity profile radionuclide flux geochronologies have been interpreted on the basis of a fluvial marine transport model which distinguishes between inputs due to direct adsorption of radionuclides onto particles in the water column and inputs resulting from the erosion of particle associated radionuclides from the drainage basin rate constants corresponding to residence times of one year for cs 137 and pu 239 240 in the water column and 1500 years for each radionuclide in the drainage basin provide reasonable agreement between the model and experimental results although there is some evidence for a slightly longer drainage basin residence time for plutonium both the threshold for the initial appearance of pu 238 derived from the atmospheric burnup of a snap 9a satellite reactor in 1964 and the magnitude of its isotopic dilution by drainage basin inputs of pu 239 240 are also in agreement with model predictions

mud volcanism and morphology of impact craters in utopia planitia on mars evidence for the ancient ocean abstract results of our detailed geological mapping and interpretation of the nature and relative and absolute model ages of units and structures in the sw portion of utopia planitia 20 45 n 100 120 e suggest the following 1 the size frequency distribution sfd of craters that both are buried by materials of the vastitas borealis units vb and superpose its surface indicate that the absolute model ages of terrain predating the emplacement of the vb is 3 7 ga 2 lack of craters that are partly embayed by materials of the vb in the sw portion of utopia planitia implies that the emplacement of the vb was faster than the rate of accumulation of impact craters and is consistent with the geologically short time of emplacement of the vb due to catastrophic release of water from outflow channels e g carr m h 1996 water on mars oxford university press new york p 229 3 the sfd of craters that superpose the surface of the vb indicates an absolute model age of 3 6 3 5 ga the absolute model ages of etched flows which represent the upper stratigraphic limit of the vb are estimated to be 3 5 ga 4 the majority of the larger i e 1 km impact craters show ejecta morphologies rampart and pancake like ejecta that are indicative of the presence of ice water in the target materials the distal portions of the pancake like ejecta are heavily degraded not due to embayment this suggests that these craters formed in targets that contained higher abundances of volatiles 5 the diameter ranges of the craters with either rampart or pancake like ejecta are overlapping from 2 to 60 km craters with pancake like ejecta are concentrated within the central portion of the utopia basin less than 1000 km from the basin center and rampart craters occur at the periphery of the basin this pattern of the crater spatial distribution suggests that materials within the center of utopia planitia contained more ice water 6 etched flows around the central portion of utopia planitia were erupted from beneath of the surface of the vb their morphology and pattern of degradation however are inconsistent with lava and instead indicate formation of the flows due to mud volcanism 7 etched flows are spatially associated with giant polygons and there is evidence that these features populated the center portion of utopia planitia before it was covered by the elysium derived units the outer southern edge of the zone of polygonal troughs and etched flows approximately corresponds to the transition from pancake like ejecta to rampart ejecta this suggest that the outer edge of the zone of the polygons and flows may outline the deeper portions of the large body 2000 km across of water ice that likely existed in the center of utopia planitia in late hesperian

oceans or seas in the martian northern lowlands high resolution imaging tests of proposed coastlines mars global surveyor mars orbiter camera images that were targeted specifically to observe locations where published accounts argue for the presence of landforms created by the interaction of a large body of water with martian topography fail to reveal any evidence to support the hypothesis that the northern lowlands were once the site of oceans or seas given the difficulty of identifying ancient coastlines on earth from orbital and aerial photography in the absence of field work this result does not preclude the possibility that mars once had large standing bodies of water on its surface but calls into question shorelines previously proposed

origin of giant martian polygons extensive areas of the martian northern plains in utopia and acidalia planitiae are characterized by polygonal terrane polygonal terrane consists of material cut by complex troughs defining a pattern resembling mudcracks columnar joints or frost wedge polygons on earth however the martian polygons are orders of magnitude larger than these potential earth analogues leading to severe mechanical difficulties for genetic models based on simple analogy arguments plate bending and finite element models indicate that shrinkage of desiccating sediment or cooling volcanics accompanied by differential compaction over buried topography can account for the stresses responsible for polygon troughs as well as the large size of the polygons although trough widths and depths relate primarily to shrinkage the large scale of the polygonal pattern relates to the spacing between topographic elevations on the surface buried beneath polygonal terrane material geological relationships favor a sedimentary origin for polygonal terrane material but our model is not dependent on the specific genesis our analysis also suggests that the polygons must have formed at a geologically rapid rate

preflow stresses in martian rampart ejecta blankets a means of estimating the water content abstract measurements of extents of rampart ejecta deposits as a function of the size of the parent craters support models which for craters larger than about 6 km diameter constrain ejecta blankets to all have a similar maximum thickness regardless of the crater size these volatile rich ejecta blankets may have failed under their own weights then flowed radially outward assuming this to be so we can then determine some of the physicomechanical properties of the ejecta deposits at the time of their emplacement finite element studies of the stress magnitudes distributions and directions in hypothetical martian rampart ejecta blankets reveal that the material most likely failed when the shear stresses were less than 500 kpa and the angle of internal friction was between 26 and 36 these figures imply that the ejecta has a water content between 16 and 72 whether the upper limit or the lower limit is more appropriate depends on the mode of failure which one presumes namely viscous flow or plastic deformation

stratigraphy and facies in the upper proterozoic damara orogen namibia based on a geodynamic model abstract the upper proterozoic damara orogen which forms a part of the pan african belt system contains a well developed geosynclinal sequence deposited 900 650 ma ago in the absence of sufficient biological and radiometric age data correlations of lithostratigraphic units across the orogen remain problematical this paper is an attempt to establish a unifying geodynamic model for the geosynclinal development of the damara orogen the model is based on the assumption that damaran geosynclinal history began with formation of continental rift structures the geosynclinal development started in the northern damara orogen with the formation of a continental rift 900 ma ago at the same time a rift dome or rift field existed in the southern part of the orogen the northern rift remained active for about 100 ma with three phases in increased differential subsidence during deposition of the nosib group the ugab subgroup and the chuos formation complex facies relationships including the ugab subgroup of the northern and the nosib group of the central orogen illustrate deposition in a shelf basin environment which had established itself after marine invasion of the northern rift subsequently the northern rift fell inactive and the northern to central orogen was affected by a phase of regional subsidence due to thermal relaxation of the stretched lithosphere the slowly subsiding region was covered by a carbonate platform karibib formation which eventually submerged giving way to the development of a wide basin in which the kuiseb formation was laid down the northern rift fell inactive when the rate of crustal stretching accompanied by rifting and differential subsidence significantly increased in the southern damara orogen 800 ma ago a trough khomas trough started to subside rapidly and was fed by turbidites from both the carbonate platform tinkas turbidites and the southern foreland of the orogen chausib turbidites only 20 30 ma later lithospheric stretching and thinning had proceeded far enough to allow crustal rupture and opening of a limited ocean matchless amphibolite this led to thermal relaxation of the lithosphere and to regional subsidence in the southern damara orogen the key for correlations across the orogen is the shift of the rifting activity from north to south this stage is marked by the development of the carbonate platform from whose southern edge the calcareous tinkas turbidites were transported into the subsiding khomas trough where pelites of the lower kuiseb formation were being laid down

pitted cones and domes on mars observations in acidalia planitia and cydonia mensae using moc themis and tes data 1 domes and cones with summit pits located in acidalia planitia and cydonia mensae were studied using moc and themis images and a tes derived thermal inertia map north of 40 5 n latitude the features have a dome like morphology and south of that latitude the morphology is more cone like layering is apparent in the summit craters of fresher looking southern cones and asymmetric aprons were observed in some instances some of the northern domes also display layering in their summit craters but asymmetric aprons were not observed the northern domes can also display multiple summit pits or no summit pits at all and can occur in association with higher albedo pancake features the northern domes are higher in albedo but have apparent thermal inertias that are lower than the surrounding plains the apparent thermal inertia values of the southern cones range from values comparable to the surrounding plains to slightly lower from the tes thermal inertia map we infer that the thermal inertia values of the pitted cones are between those of basaltic fine dust and sand while those of the surrounding plains are closer to that of basaltic sand while a unique interpretation of the origin of the pitted cones is not possible with the available data we do not find compelling evidence to suggest an origin related to either basaltic volcanism or ground ice instead an origin for these features through some combination of mud volcanism and evaporite deposition around geysers and or springs is most consistent with the observations

late cryogenian neoproterozoic glacial and post glacial successions at the southern margin of the congo craton northern namibia facies palaeogeography and hydrocarbon perspective

catchment wide soil loss from pre agricultural times to the present transport and supply limitation of erosion a high resolution record of catchment wide soil loss for the period c 1806 1990 has been obtained from little llangothlin lagoon on the new england tablelands of northeast new south wales australia the mean annual rate of mineral erosion since the time of european contact in the late 1830s was 269 t km 2 the mean rate of mineral denudation immediately prior to this was 25 t km 2a 1 in the 25 years after the arrival of the first sheep in the catchment erosion rates increased by a factor of over 50 to 1360 t km 2a 1 after c 1861 however there was an apparently sharp transition to a new low and very constant rate of denudation 52 t km 2a 1 eighty five percent of post contact erosion thus occurred in the first quarter of a century of european land use the low and constant erosion rates of the last century or more cannot be attributed to stable environmental conditions to a decrease in land use intensity or to the introduction of soil conservation measures instead it is possible that early colonial erosion almost entirely depleted the catchment of erodible material with the result that erosion moved from a transport controlled regime to one that was limited by the rate at which catchment material was made available for transport by weathering alternatively the high early colonial rates of erosion may have been associated with the extension and deepening of the drainage net during the initial phase of european contact the subsequent establishment of a new drainage net equilibrium may have reduced soil loss to a low and stable level much of the evidence available to test these competing hypotheses is equivocal nevertheless the gullying model must be rejected first because there is no evidence of past or present dissection of the catchment surface second because gullying would seem incapable of providing the highly constant rate of sedimentation that has prevailed in the basin over the past century or more and third because the gullying model cannot explain the step change from high to low rates of sedimentation in the basin further support for the supply limitation hypothesis comes from the concordance between likely rates of soil formation in the catchment and rates of sedimentation in the lagoon these conclusions have implications for our cognisance of the role of supply limitation in geomorphological processes for soil conservation practice and for our understanding of the long term impacts of agriculture on soil erosional systems

mapping of neoproterozoic source rocks of the huqf supergroup in the sultanate of oman using remote sensing abstract in recent years the neoproterozoic huqf supergroup formations of the oman salt basins have been the target for oil exploration the present study maps the surficial exposure of the huqf supergroup in and around khufai dome of the huqf area in the sultanate of oman using low cost multi spectral remotely sensed satellite data and image processing methods such as decorrelation stretching principal component analysis pca and spectral angle mapper sam as alternative to expensive and time consuming tools which have the capability and potential to be used by geoscientists for oil exploration in this research the study of advanced spaceborne thermal emission and reflection radiometer aster spectral bands 8 3 and 1 by decorrelation stretching well discriminated the masirah bay the khufai the shuram and the buah formations of the nafun group the source rocks of huqf supergroup with the quaternary deposits the analysis of visible and near infrared shortwave infrared spectral bands of aster by pca clearly showed the occurrence and spatial distribution of such formations in the rgb principal component images r pc1 g pc2 b pc3 the spatial distributions of such formations are assessed by confusion matrix after using maximum likelihood ml spectral angle mapper sam and spectral information divergence sid algorithms the matrix of ml algorithm has provided the best overall accuracy of 92 93 and kappa coefficient of 0 92 the minerals of the formations were detected by sam further the detection of such mineral groups was confirmed through the aster thermal infrared tir spectral indices image developed using the carbonate index ci quartz index qi and mafic index mi all results of image analyses are evaluated in the field and laboratory studies the study also evaluates the satellite data and image processing methods for the formations of jabal akhdar the equivalent formations of the khufai dome to show the sensor capability and the use of the image processing methods to study the source rocks the results of the study provided similar discriminations comparable to the khufai dome therefore the data and the techniques are recommended to the exploration geologists for use in similar regions of the world

magma reservoirs and neutral buoyancy zones on venus implications for the formation and evolution of volcanic landforms we examine the production of magma reservoirs and neutral buoyancy zones nbzs on venus and the implications of their development for the formation and evolution of volcanic landforms the high atmospheric pressure on venus reduces volatile exsolution and generally serves to inhibit the formation of nbzs and shallow magma reservoirs for a range of common terrestrial magma volatile contents magma ascending and erupting near or below mean planetary radius mpr should not stall at shallow magma reservoirs such eruptions would be characterized by relatively high total volumes and effusion rates for the same range of volatile contents at 2 km above mpr about half of the cases result in direct ascent of magma to the surface and half in the production of neutral buoyancy zones in general neutral buoyancy zones and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on venus than on earth for a fixed volatile content nbzs become deeper with increasing elevation over the range of elevations treated here 1 km to 4 4 km depths differ by a factor of 2 4 these analyses reveal several factors that may help to account for the low height of volcanoes on venus larger primary reservoirs cause the wide dispersal of conduits building edifices models of the position of the shallow nbz reservoir during edifice growth show that for earth the magma chamber center remains at a constant depth below the growing edifice summit thus keeping pace with the increasing elevation while on venus the chamber center becomes deeper relative to the summit of the growing edifice because of the major change in atmospheric pressure as a function of altitude therefore neutral buoyancy zones and magma reservoirs on venus will remain in the prevolcano substrate longer and in many cases may not emerge into the edifice at all the lower rate of vertical migration implies that magma reservoirs would tend to stabilize undergo greater lateral growth and become larger on venus than earth the proportion of the available magma going into production of the edifice relative to that intruded into the substrate is smaller on venus than earth large reservoirs would encourage multiple and more widely dispersed source vents and large volumes for individual eruptions in large reservoirs positively buoyant materials are likely to be produced from differentiation substrate remelting and volatile exsolution nonbuoyant materials exsolving volatiles in a shallow reservoir will need higher gas bubble concentrations to produce eruptions than on earth and when this gas enriched melt emerges at the surface it is more likely to retain its bubbles than to undergo explosive disruption due to the high surface atmospheric pressure therefore there is the potential for the production of a range of erupted lavas that have very high gas bubble concentrations leading to anomalous more viscous rheological properties inhibition of disruption of volatile rich magma for both basaltic and more evolved compositions can lead to the production of 1 more bubble rich vesicular flows characterized by higher viscosity and greater thicknesses the venus equivalent of effusions that would have lost much of their volatiles in the fire fountaining process on earth 2 high volume high discharge rate extremely gas rich basaltic effusions that increase viscosity considerably upon surface extrusion and produce domes whose volumes are considerably higher than their dense rock equivalent and 3 more evolved compositions that are gas rich but do not undergo disruption upon effusion and produce domes and flows of high viscosity the venus equivalent of terrestrial ignimbrites on the basis of these analyses we predict that intrusions and dike emplacement should be common particularly around both shallow and deep magma reservoirs and the tops of dikes should be manifested as radial fractures there should be a range of diameters of circular features associated with the presence of both shallow nbz related and deep plumerelated magma reservoirs large volume lava outpourings should be favored at lower elevations and shallow reservoirs and edifices should be more common at intermediate elevations at the highest elevations magma reservoirs are predicted to be large and relatively deep with low associated edifices direct ascent of magma where neutral buoyancy zones are unlikely low elevations and the propensity for relatively larger magma reservoirs on venus when they do form are both factors which will tend to favor high volume eruptions independent of variations in magma temperature or chemistry individual volcanic features should be interpreted in terms of regional geologic setting and the dynamics of elevation changes commonly associated with various scales of mantle processes and magma emplacement in order to assess global crustal growth processes on venus

the circum chryse region as a possible example of a hydrologic cycle on mars geologic observations and theoretical evaluation the transection and superposition relationships among channels chaos surface materials units and other features in the circum chryse region of mars were used to evaluate relative age relationships and evolution of flood events channels and chaos in contact with one another were treated as single discrete flood carved systems some outflow channel systems form networks and are inferred to have been created by multiple flood events within some outflow channel networks several separate individual channel systems can be traced to a specific chaos which acted as flood source area to that specific flood channel individual flood carved systems were related to widespread materials units or other surface features that served as stratigraphic horizons chryse outflow channels are inferred to have formed over most of the perceivable history of mars outflow channels are inferred to become younger with increasing proximity to the chryse basin in addition outflow channels closer to the basin show a greater diversity in age the relationship of subsequent outflow channel sources to the sources of earlier floods is inferred to disfavor episodic flooding due to the progressive tapping of a juvenile near surface water supply instead we propose the circum chryse region as a candidate site of past hydrological recycling the discharge rates necessary to carve the circum chryse outflow channels would have inevitably formed temporary standing bodies of h2o on the martian surface where the flood waters stagnated and pooled the chryse basin is topographically enclosed these observations and inferences have led us to formulate and evaluate two hypotheses 1 large amounts of the sublimated h2o off the chryse basin flood lakes precipitated snowed onto the flood source highlands and this h2o was incorporated into the near surface recharging the h2o sources making possible subsequent deluges and 2 ponded flood water in chryse basin drained back down an anti basinward dipping subsurface layer accessed long the southern edge of the lake recharging the flood source aquifers h2o not redeposited in the flood source region was largely lost to the hydrologic cycle this loss progressively lowered the vitality of the cycle probably by now killing it our numerical evaluations indicate that of the two hypotheses we formulated the groundwater seep cycle seems by far the more viable optimally approximately 3 4 of the original mass of an ice covered cylindrical lake albedo 0 5 1 km deep 100 km radius draining along its rim for one quarter of its circumference into substrata with a permeability of 3000 darcies can be modeled to have moved underground on timescales of the order of 10 3 years before the competing mechanisms of sublimation and freeze down choked off further water removal once underground this water can travel distances equal to the separation between chryse basin and flood source sites in geologically short approximately 10 6 year scale times conversely we calculate that optimally only approximately 40 of the h2o carried from chryse can condense at the highlands and most of the precipitate would either collect at the base of the highlands lowlands scarp or sublimate at rates greater than it would accumulate over the flood source sites further observations from forthcoming missions may permit the determination of which mechanisms may have operated to recycle the chryse flood waters

characteristics and origin of polygonal terrain in southern utopia planitia mars results from mars orbiter laser altimeter and mars orbiter camera data giant polygons on mars with several kilometers in diameter were first observed in mariner 9 and viking orbiter images and their origin formation and evolution have remained enigmatic since that time new data obtained by the mars orbiter laser altimeter mola and the mars orbiter camera moc on board the mars global surveyor spacecraft now permit analysis of topography and morphology of the polygonal terrain in unprecedented detail mola data show that 1 giant polygonal terrain in utopia is located at the lower slopes of a basin structure that is the utopia basin 2 the onset of polygonal terrain in utopia is close to the same elevation in several profiles and lies at about the same elevation as a terrace which was interpreted as a shore line of an ancient body of standing water within the utopia basin proper 3 polygonal terrain occurs over a wide range of elevations on regional slopes of 0 1 4 the depths of the troughs range from 5 m to 115 m averaging about 30 m and tend to be greater toward the center of the utopia basin 5 the mean width of polygonal troughs is of the order of 2 km ranging from 0 5 to 7 5 km data from the mars orbiter camera moc indicate that 1 the troughs are generally broad graben like features with varying morphologies i e terraces and lobateness and dimensions widths and depths 2 trough morphology has been modified by aeolian processes 3 polygonal troughs are weakly interconnected at moc resolutions and there are no smaller polygons observed within the giant polygons 4 circular depressions which are probably related to subsurface collapse sometimes occur at the bottoms of polygonal troughs 5 small scale polygonal terrain on the ejecta blankets of young craters with fluidized ejecta in the investigated area exhibits different characteristics i e smaller size presence of rims greater degree of interconnections than giant polygons in the viking images we see that 1 old impact craters are increasingly buried with younger materials toward the basin center and that 2 a large number of superposed impact craters on polygonal terrain exhibit distinctive ejecta morphologies such as rampart ejecta blankets and single and double lobate ejecta blankets mola and moc observations are consistent with the formation of polygonal terrain in the area of a former standing body of water but polygon size seems too large to be readily accounted for by desiccation or freezing processes alone on the basis of the observed characteristics we propose that the giant polygons are primarily of tectonic origin being caused by uplift of the floor of the utopia basin there are several candidates for the cause of uplift 1 the removal of the load representing former standing bodies of water water thickness estimated for the utopia basin is about 1 km in this scenario removal of this load comparable to loads placed on terrestrial continental lithosphere by the laurentide and scandinavian ice sheets by loss of the water or ice could cause uplift of the floor and polygon formation 2 the freezing and expansion of residual water buried by sediments or in the near subsurface or 3 a combination of these from the discussion of alternative models in the light of the mola and moc data we conclude that formation of giant polygons by tectonic uplift of the basin floor is most likely and deserves further investigation

evidence of ancient continental glaciation in the martian northern plains whorled ridges spaced about 2 6 km and forming lobate patterns with lobe widths of about 150 km occur at many locations in the northern plains of mars commonly in close association with sinuous troughs that contain medial ridges these landforms resemble moraines tunnel channels and eskers found in terrestrial glacial terrains such as the midcontinent of north america some martian landscapes may have formed by disintegration of continental glaciers that covered much of the northern plains into the early amazonian i e late in martian geologic history meltwater processes apparently were important in the collapse of these hypothesized ice sheets hence the glaciers apparently were wet based in part whereas striking similarities exist among areas of the northern plains and some glaciated pleistocene terrains on earth there are also important differences notably drumlin fields such as those in many glacial landscapes on earth are rare absent or not yet resolved in images of the martian northern plains another major difference is that postglacial fluvial and other water related modifications especially erosion of pleistocene terrains are substantial but similar modifications are not observed in the northern plains a virtually complete and sudden decline in the activity of liquid surface water following glaciation in the northern plains seems to be implied the climatic implications of the hypothesized martian glaciers and their decline are unclear we investigate two possibilities alternatively involving a relatively warm paleoclimate and the modern martian climate the hypothesized ice sheets in the basins within the northern plains generally at elevations lower than 1 km suggest a relationship of these frozen bodies of water with former regional lakes or seas which may have formed in response to huge discharges of water from martian outflow channels this possible relationship has been modeled glaciers may have evolved from seas by their progressive freezing and then grounding and sublimational redistribution of sea ice the transition to glaciation may have taken several million years if the climate was very cold comparable to today s or tens of thousands of years if the climate was as warm as modern antarctica a glacierized sea may have involved an extended period of glaciolacustrine and ice shelf processes

water or ice in the martian regolith clues from rampart craters seen at very high resolution abstract very high resolution viking orbiter images 8 17 m per pixel have been used to investigate the morphology of martian rampart crater ejecta blankets and the crater interiors with the objective of identifying the fluidizing medium for the ejecta and the physical properties of the target rock the occurrence of well preserved small scale pressure ridges and scour marks evidence for subsidence around isolated buried blocks in partially eroded ejecta lobes and the stability of crater walls and distal ramparts argue for ground ice being the dominant state for volatiles within the target rocks at the time of impact rare examples of channels 190 650 m wide on the surfaces of ejecta blankets and on the inner walls of the crater cerulli indicate that in some instances liquid water was incorporated into the ejecta during its emplacement no morphological evidence has been found to discount the idea that atmospheric effects were partially responsible for ejecta fluidization but it is clear that these effects were not the sole reason for the characteristic lobate deposits surrounding at least some rampart craters on mars

210pb as a chronometer and tracer burrinjuck reservoir australia cores taken at burrinjuck reservoir in southeastern new south wales have been dated using the first appearance of opb dating models reproduced the known chronology correlation analysis shows no significant relationship between original pb unsupp concentration and grain size sedimentation rate or loss on ignition differences in sediment source may explain the variations in opb a simple provenance model has been used to interpret the ratio of original opb unsupp 226ra as a tracer of topsoils and subsoils high ratios in the reservoir sediments probably indicate eroded topsoils and low ratios eroded subsoils 37cs charcoal bushfire correlations and annual grass pollen peaks none of the main

timing of post european settlement alluvium deposition in se australia a legacy of european land use in the goulburn plains the timing of landscape change post settlement alluvium psa deposition and gully erosion in the southeastern australian tablelands remains at the centre of a long standing discussion over the geomorphological effects of european land use compared with aboriginal land use and climate change few quantitative studies date the onset of gully erosion and subsequent psa deposition in the tablelands and those that do determine the timing of landscape change for individual catchments rather than across the region in this study we present optically stimulated luminescence osl burial ages of swampy meadow sm sediment and psa from six sites spread throughout the goulburn plains to place better regional constraints on the timing of landscape change psa burial ages at each of our sample sites range between 213 and 81 years before ad 2013 the year during which all samples were collected and measured corresponding to ad 1800 1932 all measured psa burial ages post date european arrival to australia and are

formation of double ring circular grabens due to volumetric compaction over buried impact craters implications for thickness and nature of cover material in utopia planitia mars 1 throughout the polygonal terrain of utopia planitia are circular grabens inferred to overlie buried crater rims thirty four of the 37 circular grabens discovered in viking and thermal emission imaging system themis images southwest of the utopia basin 21 36 n 240 265 w have two nested rings while the remaining three have a single ring all 37 circular grabens bound topographic depressions whose surface relief scales directly with diameter suggesting differential compaction of cover material within the polygonal terrain the distance of doubled circular grabens from the center of the utopia basin scales directly with the spacing between the two rings implying a relation between ring spacing and cover thickness numerical models of horizontal shrinkage during volumetric compaction of material over crater rims show two maxima of horizontal normal tension on the surface these maxima where we would expect grabens to form move away from each other with increasing cover thickness the modeled spacings of stress maxima within 1 2 km thick cover are comparable to the graben spacing observed in southwest utopia planitia implying that cover thickness in this polygonal terrain may be 1 2 km thick where cover material is thin the proximity of the two normal stress maxima may only produce a single circular graben accounting for the observation that the three single ringed grabens are most distal to the center of the basin we contend that the correlation of shrinkage model results and observed ring spacing supports a wet sedimentary origin of polygonal terrain materials consistent with the past existence of standing water in the martian lowland

iron formations related to mafic volcanism and ensialic rifting in the southern margin zone of the damara orogen namibia abstract iron formations occur within the metasedimentary metavolcanic sequence of the chuos formation in the southern margin zone of the upper proterozoic damara orogen of south west africa namibia the iron rich lithosome comprises magnetite quartz rock haematite quartz rock and magnetite quartz silicate carbonate rock on the basis of their host rock associations iron formation in diamictite sequences and in amphibolite are distinguished iron formation in amphibolite is developed both as a chemical sediment and as a composite rock consisting of chemical iron rich sediment with admixture of varying amounts of volcanic detritus iron formation in diamictite represents a pure chemical sediment both of the iron rich rocks contain abundant apatite and their manganese contents are low an exhalative origin for the iron formations of the southern margin zone related to mafic volcanism and ensialic rifting is suggested

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

redefinition of the crater density and absolute age boundaries for the chronostratigraphic system of mars abstract for the boundaries of each chronostratigraphic epoch on mars we present systematically derived crater size frequencies based on crater counts of geologic referent surfaces and three proposed standard crater size frequency production distributions as defined by a a simple 2 power law b neukum and ivanov c hartmann in turn these crater count values are converted to model absolute ages based on the inferred cratering rate histories we present a new boundary definition for the late hesperian early amazonian transition our fitting of crater size frequency distributions to the chronostratigraphic record of mars permits the assignment of cumulative counts of craters down to 100 m 1 km 2 km 5 km and 16 km diameters to martian epochs due to differences in the standard crater size frequency production distributions a generalized crater density based definition to the chronostratigraphic system cannot be provided for the diameter range used for the boundary definitions the resulting model absolute age fits vary within 1 5 for a given set of production function and chronology model ages crater distributions translated to absolute ages utilizing different curve descriptions can result in absolute age differences exceeding 10

origin of planetary wrinkle ridges based on the study of terrestrial analogs wrinkle ridges linear asymmetric topographic highs are common physiographic features on the moon mars and mercury we describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges all of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface characteristics common to both terrestrial and planetary ridges include 1 a linear asymmetric antiformal shape 2 tension cracks and grabens along the hinges of the antiform 3 overlapping en echelon lobes 4 reversals of the sense of asymmetry along strike 5 occurrence in compressional environments and 6 similarity to features produced during compression of various materials in laboratory scale models these similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface kinematic models capable of explaining the development of wrinkle ridges include 1 anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and 2 fault bend folding of upper plate rocks over the surface flattening bend of a thrust fault

an interglacial on snowball earth dynamic ice behaviour revealed in the chuos formation namibia the sturtian is the oldest ca 716 ma of three pan global glaciations in the cryogenian at omutirapo in northern namibia a 2 km wide 400 m deep palaeovalley is filled by glaciogenic strata of the chuos formation which represents the sturtian glacial record sedimentary logging of an exceptionally high quality exposure permits detailed stratigraphic descriptions and interpretations allowing two glacial cycles to be identified at the base of the exposed succession strong evidence supporting glaciation includes diamictites ice rafted dropstones and intensely sheared zones of interpreted subglacial origin these facies collectively represent ice proximal to ice rafted deposits upsection dropstone free mudstones in the middle of the succession and the absence of diamictites imply sedimentation free from glacial influence however the reappearance of glacial deposits above indicates a phase of sturtian glacial re advance comparison with age equivalent strata in south australia where evidence for sea ice free sedimentation has been established previously suggests that a sturtian interglacial may have been extensive implying global scale waxing and waning of ice sheets during a cryogenian glacial event

isidis basin site of ancient volatile rich debris layer abstract the interior plains of the isidis impact basin on mars contain landforms which have previously been interpreted as volcanic features these landforms can be classified into two broad units hillocky terrain and ridged terrain hillocky terrain the most central unit consists of isolated mounds commonly arranged in arcuate chains ridged terrain contains systems of parallel curvilinear ridges and occurs in a narrow band almost completely encircling the hillocky terrain ridges range from approximately 10 to 40 km long 0 5 to 1 0 km wide and 0 15 to 0 3 km high ridge properties and their distribution within isidis appear inconsistent with characteristics of typical volcanic fields on earth and mars alternatively we suggest that the isidis landforms reflect the deposition and subsequent removal of a thick layer of material within the basin crater statistics and the morphology of additional features within isidis provide further evidence that a major resurfacing event occurred within the basin although depositional and erosional processes are currently minimal terrestrial ice cover disintegration results in the development of landforms such as moraines kames and eskers and provides possible analogs for the features which occur in isidis the isidis cover however probably contained a vast amount of debris remained stationary throughout most of its existence and eventually sublimated thus differing from most terretrial glaciers a global survey of viking orbiter images reveals ridges elsewhere on mars with similar characteristics or spatial distribution thereby indicating that the isidis layer may have been part of a more widespread epoch of deposition this epoch possibly coincided with the period of major outflow channel formation when subsurface volatiles were released

formation erosion and exposure of early amazonian dikes dike swarms and possible subglacial eruptions in the elysium rise utopia basin region mars hundreds of narrow linear ridge segments are found in the transition zone between the elysium rise and the utopia basin occurring as both single and multiple ridges the ridges are distinctive because of their very linear steep sided nature their often sharp ridge crest which sometimes is fractured their association with stubby flows their continuity over long distances and their cross cutting of different terrain the linear ridges are interpreted to be single dikes and dike swarms either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption five dike swarms are identified having lengths ranging from 10 45 km and being between 1 7 km wide while single ridges are up to 20 km long and 100 500 m wide in the areas of dike swarms crustal dilatation is estimated to vary from 15 60 dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area the ridges both modify and constrain early amazonian flows and flood plain deposits suggesting intense dike emplacement in the early amazonian the association with different stages of inverted craters as well as some features of ice related origin possible ice cauldron and tindar like features indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement

dike indicators in the hadriaca patera promethei terra region mars abstract the eastern hellas basin rim has been highly modified by a multitude of both volcanic and fluvial processes it is covered by a large part of the circum hellas volcanic province consisting of the volcanic plains of hesperia planum and western promethei terra as well as the two central volcanoes hadriaca and tyrrhena patera and their associated lava flows large outflow channels of dao niger harmakhis reull and teviot valles dissect the wrinkle ridged plains postdating the major volcanic events the origin of these outflow channels is still ambiguous as the mobilization mechanism for the underground volatile reservoirs has yet to be revealed due to the proximity of the volcanic structures many previous studies have suggested via models that the released ice or ground water was mobilized due to endogenic heating from magmatic activity in the region to find evidence of this we conducted a systematic search for any magmatic intrusions at 50 m pixel resolution this paper provides detailed mapping of several areas where we found features which we interpret to be dikes and shows the overall distribution of such structures in the eastern hellas rim region the hadriaca patera volcano flanks exhibit a concentric pattern of linear ridges and fractures indicative of a vast ring dike system the dikes occupy mostly the area near the summit and the hellas facing flank extending there for over 400 km away from the caldera a hadriaca radial dike swarm pattern is observed extending southwards from the volcano composed of isolated parallel linear ridge group outcrops and cut by the valles canyons an additional isolated dike ridge group exists south of lower reull valles possibly controlled by the tyrrhena patera volcano some 1300 km away all dikes within the study region are roughly late hesperian in age either predating the valles formation or being roughly concurrent with them in total 500 dike segments were identified with a combined length of 2500 km since 90 of the dikes are ridges they suggest that the entire region has undergone large scale erosion of at least a few tens of meters to expose the dikes the dike orientations were most probably controlled by the volcanic centers and possibly partly by a hellas concentric fracture pattern

an ice grounding line wedge from the ghaub glaciation 635 ma on the distal foreslope of the otavi carbonate platform namibia and its bearing on the snowball earth hypothesis our detailed examination of the ghaub formation possibly 635 ma on the distal foreslope of the otavi carbonate platform is part of a regional study of the congo paleocontinental margin in northwestern namibia detrital carbonates of the ghaub formation disconformably overlie the franni aus member of the ombaatjie formation a coarsening upward stack of carbonate turbidites and oolite clast debris flow breccias interpreted to be a glacioeustatic falling stand wedge within the main ghaub formation carbonate diamictites are interleaved with mesoscale laminated to cross laminated climbing rippled grainstones and mudstones and conglomeratic carbonates amalgamation of diamictite units is observed where interleaved facies grainstones mudstones are laterally discontinuous due to reactivation of erosion followed by renewed deposition the diamictite package is progradational overall and 80 m thick on average it is overlain by the 5 15 m thick bethanis member which is unique in its lateral continuity composite fining upward trend and distinctive interbedding of turbidite grainstones argillaceous siltstones climbing rippled mudstones and meter scale stromatolite dropstones dropstones are ubiquitous within the finer grained ghaub lithofacies and their presence along with the facies context for subglacial and near grounding line deposition indicates a glacigenic origin for the ghaub formation despite its subtropical paleolatitude and distal foreslope setting we infer a glacial maximum represented by the sub ghaub disconformity followed by the main ghaub interval when an ice grounding line on the distal foreslope experienced abrupt step backs and readvances of limited magnitude terminated by the bethanis episode of unusually widespread iceberg calving and slope instability the bethanis member is overlain conformably by the keilberg member of the maieberg formation reconstruction of the foreslope places the ghaub grounding line wedge 1 3 km vertically below the rim of the platform implying an enormous base level change upon deglaciation when the platform was drowned below wave base for a period far exceeding the time scale for isostatic adjustment the magnitude of base level change supports the pan glacial hypothesis that dynamic thick ice sheets existed simultaneously on virtually all continents the snowball hypothesis that the oceans were also covered by glacial ice sea glacier provides a simple explanation for the main ghaub to bethanis transition terminal deglaciation was triggered by collapse of the sea glacier

an atmospheric blast thermal model for the formation of high latitude pedestal craters although tenuous the atmosphere of mars affects the evolution of impact generated vapor early time vapor from a vertical impact expands symmetrically directly transferring a small percentage of the initial kinetic energy of impact to the atmosphere this energy in turn induces a hemispherical shock wave that propagates outward as an intense airblast due to high speed expansion of vapor followed by a thermal pulse of extreme atmospheric temperatures from thermal energy of expansion this study models the atmospheric response to such early time energy coupling using the cth hydrocode written at sandia national laboratories results show that the surface surrounding a 10 km diameter crater 6 km apparent diameter on mars will be subjected to intense winds 200 m s and extreme atmospheric temperatures these elevated temperatures are sufficient to melt subsurface volatiles at a depth of several centimeters for an ice rich substrate ensuing surface signatures extend to distal locations 4 apparent crater diameters for a case of 0 1 energy coupling and include striations thermally armored surfaces and or ejecta pedestals all of which are exhibited surrounding the freshest high latitude craters on mars the combined effects of the atmospheric blast and thermal pulse resulting in the generation of a crater centered erosion resistant armored surface thus provide a new very plausible formation model for high latitude martian pedestal craters

diatoms as indicators of sedimentary processes in burrinjuck reservoir new south wales australia abstract a combination of high and low resolution diatom analysis conducted on a transect of five sediment cores from the downstream section of burrinjuck reservoir southern new south wales australia has revealed that despite complex sedimentation patterns there are precise correlations between diatom stratigraphies spatially dependent variation in diatom sedimentation exists particularly that resulting from density current deposition however sediments deposited in this manner are readily identified from the diatom records the nature of diatom species assemblages and their variability aid in the identification of sediment provenance and the temporal resolution of individual samples respectively the results of this study which provide a complement to other research on the reservoir should in particular allow for more accurate reconstructions of the history of nutrient concentrations in and sediment yield to the reservoir

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

mixtite deposits of the damara sequence namibia problems of interpretation abstract mixtite deposits form extensive outcrops in the pan african damara orogenic belt of namibia they occur at two different stratigraphic levels in the lower part of the upper proterozoic damara sequence south african committee for stratigraphy 1980 kroner 1981 the older varianto mixtite is confined to the northern margin of the fold belt no evidence indicating a glacigenic origin has been found but on the southern foreland of the fold belt two possibly coeval mixtite deposits court and blaubeker formation show fair evidence of such an origin the younger chuos mixtitesoccur in three separate zones of the belt all these mixtites have been interpreted as glacigenic sediments and the chuos formation has been used as a stratigraphic marker for the correlation between different parts of the fold belt the present investigation shows that 1 the mixtite deposits show no features indicating a glacial origin 2 the sedimentary features indicate deposition by gravity flow processes 3 turbidites are in several areas closely associated with and even interbedded in the mixtite deposits 4 mixtite deposition is in some areas not confined to the chuos formation proper but began at lower stratigraphic levels or persisted to a higher level 5 in some areas calcareous or dolomitic sediments are interbedded in mixtite or mixtites are interbedded in such formations the mixtites of the chuos formation are interpreted as various kinds of submarine gravity flows slump breccias mass flow slurry grain flows turbidites which were probably triggered by tectonic activity during a stage of differential subsidence that affected the whole geosyncline but was concentrated in three rift zones under this assumption the majority of the mixtites may have been deposited during a limited time spin a different model assuming synorogenic deposition of the pebbly schist mixtites of the southern margin zone is briefly discussed it is concluded that the mixtite deposits are not of glacial origin and can therefore not be regarded as reliable chronostratigraphic markers for correlations between the different facies domains of the damara sequence nor for correlation with other upper proterozoic sequences e g gariep belt katanga belt such a correlation might nevertheless exist if the extensive gravity flows should have been caused by eustatic changes of the sealevel during a time of widespread glaciation on other parts of the globe in this case local mountain glaciers might have contributed material to some of the chuos mixtites

major episodes of geologic history of isidis planitia on mars abstract we have mapped the area of isidis planitia 1 27 n 75 103 e in order to assess the geologic history of this region using modern data sets such as mola topography and the high resolution images provided by the hrsc ctx and hirise cameras results of our mapping show that the geologic history of isidis planitia consists of three principal episodes 1 impact dominated episode noachian until 3 8 ga during this time the oldest materials in the study area were formed mostly by impact reworking and mass wasting other processes e g volcanism and fluvial glacial activity likely operated at this time but played a subordinate role 2 an episode related to volcanic and fluvial glacial activities late noachian early amazonian 3 8 2 8 ga volcanism appears as the most important process at the beginning of this episode 3 8 3 5 ga and was responsible for the formation of a large circum isidis volcanic province by the early hesperian epoch volcanic materials covered large portions of the isidis rim almost completely buried the previous crater record on the floor of the isidis basin and probably were the major contributors to the filling of the basin fluvial glacial processes prevailed closer to the end of the episode early hesperian early amazonian 3 5 2 8 ga and were responsible for widespread resurfacing in the isidis planitia region mostly at 3 1 3 4 ga glaciers and or ice sheets probably resulted in a massive glaciation of the rim and the floor of the isidis basin the total volume of material eroded from the isidis rim by glacial and fluvial activity is estimated to be about 35 000 50 000 km 3 which is equivalent to a composite layer about 40 60 m thick on entire floor of the basin more important however is that the eroded materials were likely saturated with ice water and could form wet deposits on the floor 3 wind dominated episode since early amazonian 2 8 ga wind activity dominated the later geologic history of isidis planitia but resulted only in minor modification of the surface

tillites diamictites and ballistic ejecta of large impacts the primary evidence for the temporal and spatial distribution of glaciation prior to the cenozoic is the occurrence of tillites these are diamictites poorly sorted mixtures of very coarse grained to fine grained sediments and associated deposits which have features considered diagnostic of glacial action the discovery that many diamictite bearing sequences were the products of debris flows and related mass flows with contemporaneous rainout of coarse sediment has led to the reinterpretation of many tillites as glaciomarine debris flow deposits fallout of ballistic ejecta from the impact of large asteroids or comets can also create large scale debris flows with simultaneous rainout of debris recent calculations of the predicted volume and distribution of impact generated diamictites suggest that they should be common in the geologic record moreover ballistic debris flow deposits can apparently exhibit a number of features considered characteristic of glacial deposits e g striated clasts er

hillslope soil erosion estimated from aerosol concentrations north halawa valley oahu hawaii concentrations of aerosolic quartz and137cs were used to estimate rates of hillslope soil erosion during 1990 1991 in the north halawa valley on the island of oahu hawaii fluvial transport of quartz was estimated to be 6 1 mg in 1990 and 14 9 mg in 1991 fluvial transport of137cs from north halawa valley was estimated to be 1 29 109 pci in 1991 results were used with quartz contents 137cs activities and bulk densities of hillslope soils to compute rates of basinwide hillslope soil erosion ranging from 0 1 to 0 3 mm yr 1 these rates are within the range of previous estimates of denudation computed for drainage basins on oahu the aerosol concentration approach therefore is a useful method for assessing basinwide soil erosion

determining sources and transit times of suspended sediment in the murrumbidgee river new south wales australia using fallout 137cs and 210pb sediment budgets typically require an estimate of the proportional yield from erosion sources to sediments in transport and storage this becomes increasingly difficult as catchments become larger and erosion storage and deposition processes become more complex we demonstrate how fallout radionuclides can be used to estimate the proportional contributions to sediment load from a tripartite classification of erosion sources in a large catchment the mid murrumbidgee 13 500 km2 the three major potential sources of sediment within this catchment are cultivated lands 22 of the surface area uncultivated pastoral lands 78 and the numerous channels and gullies found in this region concentrations of the fallout radionuclides 210pbex and 137cs in representative samples from each of these three sources are significantly different employing these values in a simple mixing model shows that the largest contribution of material is currently derived from subsoil channel gully sources alterations to the suspended sediment 210pbex signature by in situ labeling and decay are also considered applying the model with different concentrations of 210pbex decayed as a function of residence time in channels suggests that the mean residence time of fine grained material within this system is 10 5 years however differences in 137cs concentrations observed between flood and low flow sediments and the presence of the short lived cosmogenic 7be suggest that residence time of some of this fine grained material may be of the order of only weeks to months

10be concentrations and the long term fate of particle reactive nuclides in five soil profiles from california concentration depth profiles of cosmic ray produced 10 be t 1 2 1 5m y have been measured by accelerator mass spectrometry in five soil profiles these measurements were made in an effort 1 to understand the retentivity of soil surfaces for particle reactive tracers depositing from the atmosphere on time scales of 10 4 10 6 years and 2 to explore the application of 10 be as a chronometer of geomorphic surface age the profiles sampled are from two wave cut terraces located near mendocino california a table mountain top and an alluvial fan both located near friant california the ages of the mendocino terraces are inferred to be 1 5 10 5 years based on amino stratigraphic correlations and models of terrace evolution those of the table mountain top and alluvial fan are 9 5 10 6 years and 6 0 10 5 years respectively based on k ar analyses all the surfaces sampled are nearly flat and exhibit few erosional features in addition to 10 be we measured 210 pb 239 240 pu and 7 be to ascertain the retentivity of the soils for particle reactive nuclides and to assess the present day delivery rate of nuclides from the atmosphere the 7 be inventory is 4 0 dpm cm 2 similar to those observed at nearby locations the inventories of 210 pb and pu isotopes conform to those predicted from model calculations and suggest that the soil surfaces sampled retain the entire burden of particle reactive nuclides delivered to them over short time scales 100 years the 10 be concentrations in the sample range between 0 2 and 7 10 8 atoms g soil and show strong correlations with leachable fe and or al the inventory of 10 be in the soil domain sampled is 1 2 orders of magnitude lower than that expected from the geological age of the surface and an average delivery rate of 10 be from the atmosphere 5 2 10 5 atoms cm 2 yr the low inventory of 10 be is attributed to its loss from the soil domain sampled by solution transport based on a simple model type calculation with a first order removal process for 10 be the residence time of 10 be in the soil domains sampled is determined to be of the order of 10 4 years the low residence time of 10 be in the soil domains sampled requires that it be found either deeper in the regolith or in ground waters in either case the application of 10 be as a chronometer of geomorphic surface age is severely constrained however the study of 10 be in soils provides the only entry into the long term 10 4 10 6 years behavior of particle reactive nuclides in soils and hence could be important for understanding the behavior of analogous nuclides introduced into soils by natural and anthropogenic processes

putative shorelines in northern arabia terra mars 1 three putative shorelines first proposed by parker et al 1989 are topographically and morphologically evaluated within a 700 000 km2 study area in northern arabia terra mars results are consistent with a shoreline interpretation for the arabia and deuteronilus contacts but do not support the proposed acidalia shoreline the arabia contact follows an equipotential surface with a mean elevation of 3707 m and a mean deviation of 13 m for deuteronilus results suggest that the originally proposed shoreline represents two distinct regional shorelines because two separate portions of the original deuteronilus contact approximate equipotential surfaces of 4200 m 5 m and 4000 m 6 m for both the deuteronilus and arabia contacts there is geomorphic evidence for erosion and some landforms are similar to analogous terrestrial coastal landforms these results permit but do not prove the past existence of an ocean ponded within the northern lowlands possibly as recently as the amazonian

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

resurfacing history of the northern plains of mars based on geologic mapping of mars global surveyor data 1 geologic mapping of the northern plains of mars based on mars orbiter laser altimeter topography and viking and mars orbiter camera images reveals new insights into geologic processes and events in this region during the hesperian and amazonian periods we propose four successive stages of lowland resurfacing likely related to the activity of near surface volatiles commencing at the highland lowland boundary hlb and progressing to lower topographic levels as follows highest elevations indicated stage 1 upper boundary plains early hesperian 2 0 to 2 9 km stage 2 lower boundary plains and outflow channel dissection late hesperian 2 7 to 4 0 km stage 3 vastitas borealis formation vbf surface late hesperian to early amazonian 3 1 to 4 1 km and stage 4 local chaos zones early amazonian 3 8 to 5 0 km at acidalia mensa stage 2 and 3 levels may be lower 4 4 and 4 8 km respectively contractional ridges form the dominant structure in the plains and developed from near the end of the early hesperian to the early amazonian geomorphic evidence for a northern plains filling ocean during stage 2 is absent because one did not form or its evidence was destroyed by stage 3 resurfacing remnants of possible amazonian dust mantles occur on top of the vbf the north polar layered deposits appear to be made up of an up to kilometer thick lower sequence of sandy layers early to middle amazonian in age overlain by late amazonian ice rich dust layers both units appear to have outliers suggesting that they once were more extensive

use of the geochemical record preserved in floodplain deposits to reconstruct recent changes in river basin sediment sources abstract the geochemical record preserved in overbank floodplain deposits is used in combination with a composite fingerprinting technique and the chronology provided by 137 cs dateable horizons to reconstruct recent changes in sediment sources in the exe and severn basins uk composite fingerprints for discriminating potential source materials are identified from a suite of properties including heavy metals trace metals and cation bases these fingerprints are then compared with those of historical floodplain deposits using a numerical sediment mixing model relative contributions from distinct spatial sources characterised in terms of the devonian carboniferous and permian geological sub areas of the exe and the ordovician silurian devonian carboniferous permian and triassic jurassic sub areas of the severn are shown to fluctuate over the recent past in response to intrinsic e g the occurrence of extreme hydrologic events and extrinsic e g anthropogenic disturbance associated with land use change controls the potential for fingerprint property transformation in association with floodplain storage is assessed and the scope for further research using fingerprinting to reconstruct longer term sediment sources is discussed

paired geochemical tracing and load monitoring analysis for identifying sediment sources in a large catchment draining into the great barrier reef lagoon while sediment tracing has been typically applied to identify sediment sources that are difficult to measure by gauging monitoring it can also be useful in estimating relative sediment yields from gauged river catchments the major and trace element composition of river sediments from eleven locations in the 130000 km2 burdekin river catchment northeastern australia was analysed to examine relative contributions from upstream source areas in the 2011 12water year sediment tracing results are compared against estimates derived fromsediment load monitoring at three locations comparisons show that there is good agreement between tracing results and monitoring data at one of the tributary confluences at the second site notable contrastswere found between the load estimates from the monitoring and tracing data at this site a large impoundment occurs between the upstream sampling gauging sites for source sediments and the downstream sampling gauging sites for target sediments the contrast is likely caused by temporal variations in particle size distributions of suspended sediment fromeach river and differential trapping efficiencies in the impoundment for sediment derived fromthe different tributaries in the absence of the detailed particle size data and trapping efficiency estimates sediment tracing provides the unique opportunity to elucidate source contributions of the finer fractions of suspended sediment at a third site where there were recognised measurement gaps in the monitoring data during large discharge events the relative load estimates fromthe tracing data provided a means of constraining the recognized uncertainty of monitored load estimates we conclude that sediment tracing can be used as a valuable adjunct to monitoring data particularly in remote large and data sparse catchments both tracing results and monitoring data showthat the upper burdekin river and bowen bogie riverswere the dominant source of the b10 m sediments being delivered to the gbr lagoon from the burdekin river catchment in the 2011 12 water year more substantial contribution from the belyando suttor rivers indicated by the tracing results than the monitoring data is attributed to preferential delivery of the 1 10 m sediments through the impoundment and has uncovered a knowledge gap in sediment budgets in the catchment

chryse planitia mars topographic configuration outflow channel continuity and sequence and tests for hypothesized ancient bodies of water using mars orbiter laser altimeter mola data many of the largest and most prominent outflow channels on mars debouch into chryse planitia pre mars global surveyor topographic data show chryse to be a closed depression almost 2000 km in diameter new mars orbiter laser altimeter mola data reveal the following 1 chryse is not a locally closed basin but instead opens into the north polar basin 2 the highly distinctive morphology of the six largest predominantly hesperian aged channels kasei maja simud tiu ares and mawrth disappears into the northern lowlands at average elevations that all occur within less than 170 m of a mean elevation of 3742 sd 153 m over a lateral distance in excess of 2500 km 3 the elevations where the distinctive morphology of each channel disappears all fall within 190 m of contact 2 a boundary mapped by parker et al 1993 and interpreted to represent an ancient shoreline and the mean elevation values of contact 2 and circum chryse channel termini fall within 18 m of each other in contrast the termini of seven later amazonian aged channels emerging from elysium into utopia planitia are spread over a vertical range of 1500 m 4 topographic evidence of the continuation of some of the outflow channels can be observed for distances of 250 450 km into the north polar basin but the morphology is subdued and distinctly different 5 the nature of this less distinctive topography and its crosscutting relationships show that simud and tiu are likely to represent the youngest activity specifically crosscutting ares valles 6 the distinctive change in channel morphology is consistent with rapid loss of energy encountered at base level subaerial submarine boundary and emplacement into a shallow submarine environment channel characteristics lack of distinctive deltas or lobes and continuation of subdued channel morphology suggest hyperpychnal flow and the possibility of density turbidity currents estimates of the volumes of individual channel events are wide ranging the minimum volume estimates of carr 1996 suggest that 46 such events would be required to fill the basin to the level of contact 2 and thus that the channels may have emptied into an existing standing body of water volume estimates of baker et al 1991 assume that single individual events may have filled the basin to the level of contact 2 thus requiring significant water loss between events and refilling during subsequent events to essentially the same level in both end member cases these observations are consistent with the presence of large standing bodies of water in the northern lowlands in hesperian early amazonian times

sediment source tracing using environmental magnetism a new approach with examples from australia environmental magnetism can be used for sediment source tracing in situations such as stream junctions where two catchments deliver magnetically distinguishable well combined average source mixes to a trunk stream consistent mineral magnetic parameter relationships show that spatially and temporally constant magnetic mineral assemblages occur along reaches of natural streams for most of the confluence mixing situations examined it is possible to distinguish between tributaries using magnetic parameter relationships using these relationships relative tributary contributions to the resultant downstream mix can be quantified the method can be used for tracing suspended and bedload sediments so that the principal source catchments can be determined by a sequence of measurements at stream junctions along a drainage network there is considerable potential for using this new and easily applied method for studies of sediment delivery processes and sediment movement in fluvial environments

the formation of small cones in isidis planitia mars through mobilization of pyroclastic surge deposits abstract we investigate the distinctive distribution and pattern of subkilometer sized cones in isidis planitia and their relationship to the material that fills the basin we observe that 1 the cones show uniform size spacing and morphology across the entire basin 2 they have large central depressions relative to cone basal diameters that are generally filled in and commonly show layering 3 cone chains form highly organized spatial patterns cones are also found in isolation and in dense fields 4 many adjacent chains are parallel and evenly spaced creating a pattern that mimics lava flows that have experienced compressional folding 5 no flows are associated with the cones even where summit crater rims are breached 6 the cones are at least temporally related to basin fill 7 the basin fill material is largely fine grained but with locally indurated layers at shallow depth blocks ejected by small craters from these locally indurated layers are commonly dark in color and 8 relationships between cones along a chain show no systematic temporal formation sequence along the chain we conclude that the basin was likely inundated by one or more hot partially welded pyroclastic flows devolatilization of these flows remobilized volcaniclastic material to form the cones without associated lava flows the volume of gas required to account for the observed number of cones is low and does not require the presence of ground water or ice