rate of dune reddening in a humid tropical climate the formation of red beds has long interested geologists and pedologists1 3 it has been suggested that the nature and degree of reddening in dune sands can be a useful indicator of the relative age and environmental history of the sands several authors have concluded that dune sands undergo progressive reddening with time4 7 and james and stanley8 considered that coastal dunes might actually be mapped on the basis of colour however quantitative data regarding the rate of reddening in different environmental conditions are generally lacking i present here radiocarbon evidence from north east australia which suggests that red weathering profiles have developed in stabilized dunes of holocene age in humid tropical conditions within the past 7 500 yr

sedimentology of the bondi main heavy mineral beach placer deposit murray basin southeastern australia abstract drilling and pit wall exposures at the southern end of the bondi main heavy mineral beach placer deposit provided access to the loxton parilla sands which are here divided into five lithofacies the depositional environment of each lithofacies is interpreted as shoaling zone breaker zone surf zone swash zone and backshore dune other units encountered include the duddo limestone loddon river group bookpurnong formation and shepparton formation the interpreted depositional environments for these units are respectively shallow marine fluvial shallow marine shelf and fluvio lacustrine a palaeogeographical model is presented which proposes that the bondi main deposit formed at the southern end of a north trending shoreline this shoreline was truncated to the south by the dundas tableland and is broadly analogous in its geomorphological setting to the modern geographe bay in western australia the deposit therefore appears to have formed in association with a heavy mineral trap at its southern end postdepositional weathering overprints include ferruginous mottling clay eluviation and possibly quartz fracturing and disaggregation the ferruginous mottles formed under spatially and temporally variable redoximorphic conditions with fe being derived from the weathering of fe bearing primary minerals particularly ilmenite postdepositional clays in the loxton parilla sands are interpreted as being derived from the overlying shepparton formation

processes of selective grain transport and the formation of placers on beaches placers are found on many beaches of the oregon coast in the beach that is the focus of this study the principal placer minerals are ilmenite 22 0 epidote 20 0 garnet 18 7 augite 15 5 hypersthene 8 1 hornblende 5 8 and zircon 2 0 the ilmenite fraction actually being partly chromite a series of beach face sand samples was obtained along a profile when sand was being eroded from the upper beach and transported to offshore bars since the processes of grain selective sorting leading to placer formation were probably most active at such a time the landward most sample contained 96 heavy minerals being part of the placer this concentration systematically decreased offshore to a 6 heavy mineral content in the seaward most sample 54 m offshore determinations of individual heavy mineral concentrations revealed that although they all tended to become concentrated within the placer with light quartz and feldspar dominating the offshore transport the sorting processes were m

rootless tephra stratigraphy and emplacement processes volcanic rootless cones are the products of thermohydraulic explosions involving rapid heat transfer from active lava fuel to external sources of water coolant rootless eruptions are attributed to molten fuel coolant interactions mfcis but previous studies have not performed systematic investigations of rootless tephrostratigraphy and grain size distributions to establish a baseline for evaluating relationships between environmental factors mfci efficiency fragmentation and patterns of tephra dispersal this study examines a 13 55 m thick vertical section through an archetypal rootless tephra sequence which includes a rhythmic succession of 28 bed pairs each bed pair is interpreted to be the result of a discrete explosion cycle with fine grained basal material emplaced dominantly as tephra fall during an energetic opening phase followed by the deposition of coarser grained material mainly as ballistic ejecta during a weaker coda phase nine additional layers are interleaved throughout the stratigraphy and are interpreted to be dilute pyroclastic density current pdc deposits overall the stratigraphy divides into four units unit 1 contains the largest number of sediment rich pdc deposits units 2 and 3 are dominated by a rhythmic succession of bed pairs and unit 4 includes welded layers this pattern is consistent with a general decrease in mfci efficiency due to the depletion of locally available coolant i e groundwater or wet sediments changing conduit vent geometries mixing conditions coolant and melt temperatures and or coolant impurities may also have affected mfci efficiency but the rhythmic nature of the bed pairs implies a periodic explosion process which can be explained by temporary increases in the water to lava mass ratio during cycles of groundwater recharge

the acidalia mensa region on mars a key element to test the mars ocean hypothesis abstract we present the results of a detailed photogeological study of a region surrounding acidalia mensa 43 50 n 15 35 w based on analysis of a mosaic of the ctx images nominal resolution 5 m px the main result of the study is the unfolding of the geologic history of the study region and determination of absolute model ages of its major episodes the documented history begins with the formation of a volcanic plateau of acidalia mensa 4 ga ago the surface of the acidalia plateau was strongly modified since its formation the crater size frequency distribution csfd on the plateau indicates that the resurfacing was likely consisted of multiple episodes the latest such episode recognizable by the crater statistics occurred 3 65 ga ago the vast majority of the surface around acidalia mensa is covered by materials of the background plains that correspond to the interior unit of the vastitas borealis formation vbf the csfd on the background plains corresponds to an absolute model age ama of 3 58 ga which is completely within the range of amas determined for the vbf along its boundary with the southern uplands small scale features such as bright cones mounds polygonal troughs and flow like mantling materials postdate the emplacement of the background plains and manifest the post formational evolution of the vbf the majority of crater ejecta in the study area have higher albedo in the ctx and hirise images but appear as dark spots in the themis ir nighttime images these wavelength dependent properties of the ejecta indicate the presence of light toned and fine grained material beneath the surface of the background plains this material was the source of numerous bright cones mounds we interpret the formation of this reservoir as the result of sorting of large amounts of water mud deposited in the study area and by implication within the northern lowlands the final episodes of the ancient geologic history of the study area were related to the emplacement of materials of the thick flows at topographically high levels within the acidalia plateau 3 47 ga ago the morphology of the flows is inconsistent with lava and we interpret the occurrences of the thick flows as the result of displacement of water saturated regolith in the form of either soli or gelifluction flows or ice cored rock glaciers

fate of outflow channel effluents in the northern lowlands of mars the vastitas borealis formation as a sublimation residue from frozen ponded bodies of water 1 we analyze the fate of the hesperian aged outflow channel effluents emplaced into the northern lowlands of mars we have modeled the evolution of these effluents under the assumption that they were emplaced under a range of atmospheric conditions comparable to those of today and thought to have prevailed in the hesperian under these conditions we find that the evolution of the sediment loaded water after it left the channels includes three phases phase 1 emplacement and intensive cooling violent emplacement of water followed by a short period of intensive evaporation from the surface and near surface layer and intensive convection during this phase the water maintained and redistributed its large suspended sediment load water vapor strongly influenced the climate at least for a geologically short time when the temperature of the water reached the temperature of the maximum density or the freezing point boiling and intensive convection ceased and the water deposited the sediments phase 2 freezing solid geologically rapid freezing of the water body accompanied by weak convective water movement occurred over a period of the order of 104 years phase 3 sublimation and loss this period involved sublimation of the ice and lasted longer than the freezing phase the rate and latitudinal dependence of the sublimation as well as the location of water vapor condensation crucially depend on the planetary obliquity climate and sedimentary veneering of the ice phase 3 would have been very short geologically 105 106 years if an insulating sedimentary layer did not build up rapidly if such an insulating layer did form rapidly sublimation could cease and residual ice hundreds of meters thick could remain below the surface today the northern lowlands of mars are largely covered by the late hesperian aged vastitas borealis formation vbf which has sharp boundaries clearly seen in the map of kilometer scale roughness and a distinctive kilometer scale roughness signature we examine detrended topography data and find evidence that the vbf is underlain at very shallow depths by an early hesperian ridged volcanic plains substrate rather than frozen water deposits remaining from the outflow channel events analysis of the vbf roughness characteristics suggests at least 100 m thickness of sediments on top of the underlying volcanic ridged plains the total inferred volume of the vbf material approximately corresponds to the volume of material removed from the outflow channels these results support a model in which the vastitas borealis formation predominantly represents the sedimentary residue remaining after the sediment laden water effluents of the outflow channels ponded in the northern lowlands and rapidly froze solid and sublimed the distinctive facies of the vbf are interpreted to be related to the freezing sublimation and residue of the outflow channel effluents ridged facies are dominantly marginal and are interpreted to be related to ice sheet lateral retreat knobby facies occur throughout and are interpreted to be due to a variety of causes including dewatering de icing and brine related processes and kame like ice residues grooved facies are interpreted to represent postsublimation uplift and fracturing due to load removal the mottled facies may represent bright ejecta whose albedo is related to buried sedimentary or evaporitic residues presently the most likely sites to find frozen remnants of the hesperian ocean are below the floors of stealth craters underlying the vbf on the basis of these findings and interpretations we make predictions for the fate of the outflow channel water vapor and the nature of the martian hydrologic cycle during the hesperian if noachian aged oceans existed conditions at that time would be similar to those described for a hesperian ocean as soon as a global cryosphere was formed if any residual deposits remain in the northern lowlands from a proposed noachian ocean they would lie below both the vbf and the underlying sequence of hesperian ridged plains

spatial and temporal variability of titanomagnetite placer deposits on a predominantly black sand beach abstract titanomagnetite forms rich placer deposits along the northwest coast of new zealand these deposits were sampled along 3 shore normal transects spaced over the southern 2 km of a dissipative high energy beach on the west coast in 5 field campaigns covering one year the percentage of opaque minerals mainly titanomagnetite was extremely high in the upper 30 m of the beach face extending seaward where these opaque minerals were gradually replaced with variable amounts of lighter augite hornblende and plagioclase the pattern appeared to be divided into two regions a lower seaward and an upper landward region separated by a point where either marine dominated over aeolian processes or where swash dominated over breaking processes in the seaward region the percentage of opaques increased and particle size fined landward as undertow removed the lighter larger particles seaward in the landward region the percentage of opaques and particle size were more constant or even showed the reverse pattern as wind transported the lighter material shoreward or swash asymmetry transported the heavier material seaward the similarity of settling velocities over the whole beach face suggests that sorting by size rather than weight plays a dominant role in separating the mineral assemblages considerable variations existed between transects this could be explained by the spatial changes in surfzone waves and currents that were associated with proximity to the southern headland and various rip current channels that characterised this dissipative site surprisingly the percentage of opaques decreased when the wave conditions of the day of sampling were more energetic in contrast to many other placer deposits these deposits are abundant on the beach face forming an armouring layer during lower wave energy conditions during higher wave conditions the surface layer erodes allowing lighter augite plagioclase and hornblende to be released from the sediments below

thermophysical properties of the isidis basin mars 1 we investigated the thermal properties of the isidis basin in order to understand the high values 450 j m 2 k 1 s 1 2 located in the southern region of the basin thermal inertia data were compared to a variety of complementary data sets including radar visible and results from mesoscale atmospheric simulations we considered four mechanisms for creating the high thermal inertia including 1 the thinning of a dust mantle 2 the presence of unconsolidated coarse grained material 3 high rock abundance and 4 a high degree of induration induration is the scenario most consistent with the data although we cannot rule out unconsolidated materials and it is likely that rocks contribute to values of thermal inertia to a lesser degree we also investigated three mechanisms for controlling the geographical distribution of the high thermal inertia values including 1 the influence of topography 2 the role of surface morphology and 3 present aeolian processes topography plays a significant role along the southern boundary of the basin but not within the basin itself themis data show a complex relationship between the thermal inertia and morphology the wind patterns modeled by the mars regional atmospheric modeling system mrams are not fully consistent with the wind directions implied by streaks in the thermal data but are consistent with a second group of streaks observed in the visible data this suggests that small scale tens of kilometers streaks observed in the thermal data did not form under present day nominal winds

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

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

landscape formation at the deuteronilus contact in southern isidis planitia mars implications for an isidis sea abstract two of the most widely studied landforms that are associated with a putative ocean that filled the northern hemisphere of mars are 1 the vastitas borealis formation vbf plain units that cover a larger portion of the northern lowlands of mars and 2 a candidate paleoshoreline e g the deuteronilus contact which represents the outer margin of the vbf the vbf and the deuteronilus contact are interpreted to result from a short lived late hesperian ocean that readily froze and sublimated similar landforms are also present in the impact basin of isidis planitia and suggest formation processes comparable to those that formed the vbf and the deuteronilus contact in the northern lowlands our study of the deuteronilus contact in isidis revealed geologic evidence that possibly supports the existence of a late hesperian early amazonian isidis sea for example numerous valleys that are incised into the plains of the southern isidis basin rim between 82 90 e and 3 6 n and trend a few tens of kilometers to the north following the general topographic gradient toward the center of isidis planitia a few of them reach the deuteronilus contact and continue as sinuous ridges in the isidis interior plains iip based on our findings we conclude that the geologic setting along the deuteronilus contact including the valleys and ridges is a result of 1 late hesperian short term fluvial activity 2 a late hesperian early amazonian short lived isidis sea that readily froze 3 subglacial drainage and esker formation and 4 subsequent sublimation of the proposed isidis ice sheet although the fluvio glacial model we introduce in our manuscript cannot fully explain the geologic setting possible alternative formation models including relief inversion and fluvio volcanic scenarios are even less capable in explaining the observed geologic setting along the deuteronilus contact

possible pingo fields in the utopia basin mars geological and climatical implications abstract the presence of pingos on mars has been hypothesized since the period of the viking mission in fact a diverse range of pingo like features has been found at various martian sites including elysium chryse and utopia planitiae in the northern lowlands due to the morphology and the geological setting some of those features were interpreted in different ways creating some controversies as happened in athabasca valles this reflects the complexity of interpreting these features by remote sensing and multiple plausible interpretations of the same feature with the objective of identifying new possible pingos or rootless cones on mars we selected a study area in utopia planitia 10 55 n 210 260 w where the presence of both features is possible due to its geological history volcanic and hydrological we analyzed more than 2100 mars orbiter camera moc narrow angle images in addition to viking thermal emission imaging system themis and high resolution stereo camera hrsc images together with mars orbiter laser altimeter mola derived digital elevation models dems with a geographic information system gis we found in 94 moc narrow angle images dome cone and ring shaped features we analyzed them from morphological and morphometrical points of view in order to compare them with relevant features on mars and earth we tested different possible origins for those features following the approach of multiple working hypotheses we conclude that the dome cone and ring shaped features could be pingos which is in agreement with their geological settings regarding the driving heat source for the formation of the purported pingos we propose the existence of a heat source possibly a magma chamber underneath the surface of the utopia basin together with possible climatic shifts the past activities of the heat source may have caused melting of ground ice the pingo growth due to freezing of the water would have occurred during the following cold climatic conditions

quantitative heavy mineral analysis of a pliocene beach placer deposit in southeastern australia using the autogeosem abstract thirty two heavy mineral separates each comprising approximately 2000 grains were analyzed using the automatic geological scanning electron microscope autogeosem this analysis was undertaken to study the influence of depositional environment on the distribution of heavy minerals throughout a regressive pliocene coastal sequence the majority of these heavy minerals were separated from the loxton parilla sands the host of the bondi main heavy mineral beach placer deposit in the murray basin of southeastern australia the remaining heavy minerals were separated from a number of other neogene units encountered at the deposit the heavy mineral suite is dominated by stable to ultrastable minerals such as zircon rutile and tourmaline along with ilmenite various intermediate titanates and anatase sillimanite andalusite topaz chrome spinel chromite monazite and muscovite also occur these heavy minerals are heterogeneously distributed throughout both the loxton parilla sands and the remaining neogene units the main process controlling the heterogeneous distribution of these heavy minerals throughout the loxton parilla sands appears to have been the hydraulic conditions which are intimately linked with the environment of deposition consequently the dense heavy minerals density 3 5 g cm3 are concentrated in relatively high energy environments such as the breaker zone and swash zone the less dense heavy minerals density 3 5 g cm3 are concentrated in the shoaling zone and shelf environments the erratic distribution of the various heavy minerals in some of the other neogene units is also apparently due to varying depositional conditions postdepositional weathering has altered the heavy mineral assemblages in all units accordingly some primary minerals such as ilmenite appear to have altered to secondary minerals such as pseudorutile and anatase

syrtis major and isidis basin contact morphological and topographic characteristics of syrtis major lava flows and material of the vastitas borealis formation received 18 october 2002 revised 10 march 2003 accepted 14 april 2003 published 28 june 2003 1 the floor of isidis basin is covered by materials of the vastitas borealis formation vbf that appear to be emplaced essentially as a single unit along its western boundary isidis basin is in contact with volcanic flows from syrtis major planum the contact between the isidis unit and volcanic flows from syrtis major is sharp to gradational and in places is characterized by a high 500 m scarp or by a network of faults that separate pieces of lava plains off the main plateau of syrtis clusters of knobs and mesas sometimes arranged in flow like features are also typical features of the transition zone several important characteristics of the transition from syrtis major to isidis basin are documented 1 the small scale surface texture seen in moc images appears to be the same for both the syrtis lava plateau and the knobs and mesas that characterize the transition 2 there is strong evidence for the breakup of the coherent surface of syrtis major where it is in contact with materials in isidis basin 3 the plateau breakup the knobby terrain occurs basinward after the major break of slope of syrtis major where it enters the isidis basin 4 there is no evidence for plateau breakup anywhere up on the slopes of syrtis major planum 5 the lavas of syrtis remain morphologically intact where they are in contact with other units such as the noachian cratered terrain or where lava flows are stacked within syrtis major itself these characteristic features of the transition zone from syrtis to isidis are readily explained if the zone of plateau breakup consists of relatively young lava flows that have been superimposed onto the surface of a volatile rich substratum such as the interior unit of isidis basin the vastitas borealis formation thus simple superposition of volcanic materials on top of volatile bearing sediments can explain the key geological and topographic aspects of the transition zone from syrtis major to isidis basin on the basis of our findings we outline the following scenario for the evolution of this region in the early hesperian volcanic plains are emplaced in syrtis major the lower part of the syrtis major formation and wrinkle ridges deform their surfaces soon thereafter concurrently volcanic plains are emplaced on the floor of the isidis basin and wrinkle ridges deform their surfaces soon thereafter the apparent simultaneity of these units may mean that syrtis major was the source of many of the flows in the isidis basin in the early part of the upper hesperian subsequent to the formation of most of the wrinkle ridges the vastitas borealis formation was emplaced in the isidis basin and elsewhere in the northern lowlands following the emplacement of the vastitas borealis formation the upper part of the syrtis major formation was emplaced erupting from the eastern margins of syrtis major planum and flowing down into the westernmost part of the isidis basin on top of the recently emplaced vastitas borealis formation modification of the superposed lavas by degradation and evolution of the vbf formed the scarps and unusual morphology of the marginal areas we found no compelling evidence for massive or sudden erosion from syrtis major to produce the plains currently on the surface of the floor of the isidis basin the vastitas borealis

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

age relationship of basaltic and andesitic surface compositions on mars analysis of high resolution tes observations of the northern hemisphere 1 previous mars global surveyor thermal emission spectrometer tes results have identified two principal surface compositions on mars basaltic surfaces are found primarily in the southern highlands while andesitic surfaces are found in the northern lowlands and in smaller concentrations distributed throughout the southern highlands in 1 pixel per degree composition maps the exact boundary between the basaltic and andesitic compositions is obscured by large amounts of equatorial surface dust in this work high resolution tes surface spectral data are used to identify and characterize isolated regions of basalt within the equatorial dust regions and northern lowlands generally between 20 s 60 n 0 360 w in an effort to better understand the nature of the boundary between the two compositions the purpose of refining this boundary is to more accurately determine the relationship of the compositional dichotomy with global surface morphology and derived crustal thickness results show that the basaltic surface composition is closely associated with the ancient cratered terrain morphology but is not well correlated with crustal thickness the northern extent of the tes basalt composition is also established with four exceptions there are no significant concentrations 30 surface cover of basalt greater than 400 km2 in area within the northern plains three are located within or adjacent to knobby terrain which has been suggested to be erosional remnants of the cratered highlands the fourth exception is in milankovic crater and may represent a local basalt flow or basaltic material excavated during crater formation results from this work suggest that there is a stratigraphic relationship between the basaltic and andesitic surface compositions with younger andesitic materials overlying older basaltic materials throughout the equatorial and northern plains regions

evidence for igneous activity and implications for the origin of a fretted channel in southern ismenius lacus mars northern arabia terra mars is characterized by a complex landscape that includes fretted terrain fretted channels completely closed canyons shallow troughs and fracture bounded depressions the importance of ground ice in the initiation and development of these features and of large impact structures in controlling channel courses has long been recognized the development of the fretted channel systems including the integration of closed canyons craters and surface depressions into throughgoing channels has previously been attributed primarily to mass wasting processes the two channel systems in southern ismenius lacus quadrangle mamers valles and ismeniae fossae incorporate craters of probable impact origin but both also include irregular crater like features and scalloped channel reaches that have characteristics not consistent with an impact origin some of these are by analogy with morphologically similar features on earth and elsewhere on mars reasonably interpreted as of volcanic origin the detailed morphologies of a few diagnostic features associated with ismeniae fossae suggest a hydrovolcanic origin an inference supported by the probable presence of abundant ground ice or groundwater at the time of their formation the evidence described here for hydrovolcanism supports the inference that in addition to mass wasting processes explosive excavation intrusion driven sublimation subsurface erosion and erosion by running water may have played important roles in channel formation and evolution as well all of these processes are consistent with magma interacting with groundwater or ground ice

valleys paleolakes and possible shorelines at the libya montes isidis boundary implications for the hydrologic evolution of mars abstract we describe the results of our morphologic stratigraphic and mineralogic investigations of fluvial landforms paleolakes and possible shoreline morphologies at the libya montes isidis planitia boundary the landforms are indicative of aqueous activity and standing bodies of water including lakes seas and oceans that are attributed to a complex hydrologic cycle that may have once existed on mars in the noachian 3 7 ga and perhaps also in the hesperian 3 1 ga our observations of the libya montes isidis planitia boundary between 85 86 5 e and 1 8 5 n suggest that 1 the termination of valley networks between roughly 2500 and 2800 m coincide with lake size ponding in basins within the libya montes 2 an alluvial fan and a possible delta layered morphologies and associated al phyllosilicates identified within bright polygonally fractured material at the front of the delta deposits are interpreted to be the results of fluvial activity and discharge into a paleolake 3 the arabia shoreline appears as a series of possible coastal cliffs at about 3600 and 3700 m indicating two distinct still stands and wave cut action of a paleosea that temporarily filled the isidis basin the early hesperian and 4 the deuteronilus shoreline appears at 3800 m and is interpreted to be a result of the proposed sublimation residue of a frozen sea that might have filled the isidis basin similar to the vastitas borealis formation vbf identified in the northern lowlands we interpret the morphologic geologic setting and associated mineral assemblages of the libya montes isidis planitia boundary as results of fluvial activity lake size standing bodies of water and an environmental change over time toward decreasing water availability and a cold and dry climate

origin of coarsely crystalline gypsum domes in a saline playa environment at the white sands national monument new mexico 1 dome like structures up to 3 m in height composed predominantly of coarse crystals of selenite gypsum occur on the surface of alkali flat a saline playa lake in white sands national monument new mexico the structures were investigated using field observations aerial images and geochemical methods the domes are inferred to be remnants of lake sediments that have been preserved from holocene eolian erosion due to higher cementation resulting from crystallization of large gypsum selenite crystals in the playa s clay rich sediments low 2h values of the selenite from 90 to 69 suggest precipitation from saturated solutions associated with groundwater seepage in the playa related to the upward flows of groundwater primarily fed by meteoric water rather than the evaporation of the playa water values of 34s for selenite range from 12 1 to 13 8 median 13 0 and are notably higher than the dissolved sulfate in the modern groundwater system that has 34s values from 10 2 to 11 8 median 11 4 the two main regional sources of sulfate are middle permian evaporites with median 34s values of 12 0 and lower permian evaporites with median 34s values of 13 0 the 34s values measured in domes suggest their formation during a period of time when groundwater seepage might have been dominated by deeply circulating water that interacted with lower permian evaporites buried in the basin center the apparent alignments of domes suggest that past groundwater seepage was controlled by fractures beneath alkali flat which are associated with a regional fault system in the area

identity and emplacement of domical structures in the western arcadia planitia mars 1 morphologic morphometric and thermophysical aspects of domical structures in a restricted part of the mars northern plains were characterized using mars odyssey and mars global surveyor data the majority of domical structures consist of relatively high thermal inertia subcircular to irregularly shaped core bodies surrounded by adjacent relatively low albedo low thermal inertia annuli and dispersed aureoles of apparently disaggregated material core profiles vary considerably from low to high aspect ratios elongate arms of material extend from the central summit regions in some of the structures core features include apparent blocky surface texture summit fissures and pits apparent summit and flank ruptures suggestive of eruption of material and concentric and straight summit ridges core heights range from 30 to 400 m mean 160 m diameters range from 620 to 3090 m mean 1550 m aspect ratios range from 0 02 to 0 36 mean 0 11 and volumes range from 0 1 to 1 8 km3 an additional morphologic type consists of subcircular domical mounds that are apparently covered by plains materials we propose that the majority of the structures are partially extrusive cryptodomes and lava domes whereas the mounds are entirely intrusive cryptodomes

identification of volcanic rootless cones ice mounds and impact craters on earth and mars using spatial distribution as a remote sensing tool 1 this study aims to quantify the spatial distribution of terrestrial volcanic rootless cones and ice mounds for the purpose of identifying analogous martian features using a nearest neighbor nn methodology we use the statistics r ratio of the mean nn distance to that expected from a random distribution and c a measure of departure from randomness we interpret r as a measure of clustering and as a diagnostic for discriminating feature types all terrestrial groups of rootless cones and ice mounds are clustered r 0 51 0 94 relative to a random distribution applying this same methodology to martian feature fields of unknown origin similarly yields r of 0 57 0 93 indicating that their spatial distributions are consistent with both ice mound or rootless cone origins but not impact craters each martian impact crater group has r 1 00 i e the craters are spaced at least as far apart as expected at random similar degrees of clustering preclude discrimination between rootless cones and ice mounds based solely on r values however the distribution of pairwise nn distances in each feature field shows marked differences between these two feature types in skewness and kurtosis terrestrial ice mounds skewness 1 17 1 99 kurtosis 0 80 4 91 tend to have more skewed and leptokurtic distributions than those of rootless cones skewness 0 54 1 35 kurtosis 0 53 1 13 thus nn analysis can be a powerful tool for distinguishing geological features such as rootless cones ice mounds and impact craters particularly when degradation or modification precludes identification based on morphology alone

phyllosilicate and hydrated silica detections in the knobby terrains of acidalia planitia northern plains mars here we report detections of fe mg phyllosilicates and hydrated silica in discrete stratigraphic units within the knobby terrains of acidalia planitia made using data acquired by compact reconnaissance imaging spectrometer for mars fe mg phyllosilicates are detected in knobs that were eroded during southward retreat of the dichotomy boundary a second later unit now eroded to steep sided platforms embaying the knobs contains hydrated silica which may have formed via localized vapor weathering thin film leaching or transient water that resulted in surface alteration these are then overlain by smooth plains with small cones hypothesized to be mud volcanoes which previous studies have shown to have no hydrated minerals in spite of acidalia s location within the putative northern ocean collectively the data record a history of aqueous processes much like that in the southern highlands with progressively less intensive aqueous chemical alteration from the noachian to amazonian

surface and crater exposed lithologic units of the isidis basin as mapped by coanalysis of themis and tes derived data products 1 the stratigraphy and mineral heterogeneity of surface and crater exposed deposits in the southwestern portion of the isidis basin were investigated using spatial spectral visible and thermophysical data sets from both the mars global surveyor and odyssey missions four themis spectral surface units were identified progressing from the libya montes highlands to the inner lowland plains of isidis planitia lithologic determinations of these spectral units were made by linear deconvolution analysis of tes data olivine rich surface materials correlate with a well documented high thermal inertia unit based on spatial and stratigraphic relationships interpreted from both crater exposed and surface exposures the olivine rich unit was determined to have formed subsequent to the isidis basin forming event morphology occurrence and linear deconvolution of this unit suggests that it may represent noachian age to hesperian age picritic lavas that erupted as early stage lavas originating from sources such as syrtis major beneath isidis and as far as tyrrhena patera these lavas are suggested to have partially filled the basin based on crater exposed occurrences and were subsequently buried by further evolved olivine poor lavas later these lavas were exposed by erosion and subsequent impacts into the basin crater scaling suggests significant infilling of the basin by these lavas that may account for craters with very high d d ratios and the well developed positive mass anomaly associated with the basin this study also demonstrates that the remote sensing of impact craters in conjunction with surface mapping is a potent mapping tool for understanding stratigraphy and the petrogenesis of the martian crust

modeling steam pressure under martian lava flows abstract rootless cones on mars are a valuable indicator of past interactions between lava and water however the details of the lava water interactions are not fully understood limiting the ability to use these features to infer new information about past water on mars we have developed a model for the pressurization of a dry layer of porous regolith by melting and boiling ground ice in the shallow subsurface this model builds on previous models of lava cooling and melting of subsurface ice we find that for reasonable regolith properties and ice depths of decimeters explosive pressures can be reached however the energy stored within such lags is insufficient to excavate thick flows unless they draw steam from a broader region than the local eruption site these results indicate that lag pressurization can drive rootless cone formation under favorable circumstances but in other instances molten fuel coolant interactions are probably required we use the model results to consider a range of scenarios for rootless cone formation in athabasca valles pressure buildup by melting and boiling ice under a desiccated lag is possible in some locations consistent with the expected distribution of ice implanted from atmospheric water vapor however it is uncertain whether such ice has existed in the vicinity of athabasca valles in recent history plausible alternative sources include surface snow or an aqueous flood shortly before the emplacement of the lava flow

landform assemblage in isidis planitia mars evidence for a 3 ga old polythermal ice sheet abstract the floor of isidis planitia a giant impact basin located close to the martian equator exhibits a landform assemblage nicknamed thumbprint terrain made of arcuate ridges aligned cones isolated cones cone fields associated with a peripheral network of sinuous ridges linear depressions and mounds from a new comprehensive mapping initiative of these landforms and from comparisons with terrestrial analogues ribbed moraines dirt cones kettle holes eskers tunnel valleys and moraine plateaux we demonstrate that this distinctive assemblage is a glacial landsystem inherited from the presence of a massive polythermal ice sheet over the basin during the hesperian the flow of the ice sheet was controlled by its basal thermal regime wet based conditions led to the formation of arcuate ridges and aligned cones in most parts of the basin while a negative geothermal anomaly due to impact related crustal thinning was responsible for cold based conditions in its central part where only isolated cones and cones fields are present sinuous ridges linear depressions and mounds at the basin margins are interpreted as relicts of a radial network of subglacial channels which drained the glacial meltwater produced within the interior of the ice sheet across its cold based periphery

geologic context of the mars radar stealth region in southwestern tharsis stealth is a region on mars that has no distinguishable radar return stealth was discovered in 1988 by muhleman et al 1991 in 3 5 cm earth based radar images and it was found to extend 2000 km along the martian equator west of arsia and pavonis montes stealth was proposed to be a deposit of unconsolidated granular material with a minimum thickness of several meters with the most likely explanation being that stealth is a volcanic tephra deposit muhleman et al 1991 1995 stealth overlies some of the youngest geologic units on mars including lava flows and a giant curvilinear ridged lobate unit on the west flank of arsia mons stealth also overlies part of a region of smooth and wind scoured materials called the medusae fossae formation examination of high resolution viking orbiter images suggests that stealth is the youngest of several discontinuous wind worked mantles of fine grained 1 cm sediment older deposits of fine sediment appear to be interbedded with lava flows and show evidence of aeolian deposition dunes and deposits in the lee of topographic obstacles and erosion yardangs and pedestal craters the geologic context supports a volcanic ash origin for stealth if stealth is composed of tephra then its extent and the nature of landforms in the region indicate that it resulted from multiple eruptions that occurred relatively late in martian history possible source vents include linear depressions flanked by constructive volcanic landforms that are located on the lower western slopes of arsia and pavonis montes

the record of pliocene sea level change at enewetak atoll abstract detailed seismic stratigraphy lithostratigraphy and chemostratigraphy indicate that atoll wide subaerial exposure surfaces major disconformities developed during major sea level lowstands form prominent seismic reflectors and are coincident with biostratigraphic breaks in the plio pleistocene on enewetak atoll sea level models based on the stratigraphic position and age of major disconformities suggest a maximum sea level highstand elevation of 36 m above present sea level and a maximum sea level lowstand elevation of 63 m below present sea level for the pliocene

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

geological and exploration models of beach placer deposits integrated from case studies of southern australia abstract the processes leading to the formation of beach placer deposits generally begin inland and terminate at the coast including source rocks being weathered eroded and then transported by streams and rivers to the coast where the sediments are deposited in a variety of coastal environments the coastal sediments are reworked by the action of waves tides longshore currents and wind which are effective processes for sorting the mineral grains based on differences in their size and density resulting in laminated or lens shaped packages of sediments up to tens of meters thick that are rich in heavy minerals detailed studies of sedimentary basins as well as peripheral paleo valleys that drained sediment source areas are important tools in the exploration for heavy mineral resources knowledge of the paleo basin associated valley architecture and the source of heavy minerals concentrated in the shorelines and valleys are useful guides to the potential for and location of economic deposits evidence from sedimentology can be combined with that from other geological and geophysical characteristics to arrive at a general reconstruction of basin and paleovalley architecture and depositional environments complex paleogeography of the shorelines can influence or determine the sites of heavy mineral concentration heavy mineral sands tend to concentrate in certain shoreline settings during storm activity repeated storm erosion and reworking over centuries e g the southeastern coast of australia or millennia e g the eucla and murray basins of australia can progressively enrich heavy mineral sand deposits preservation of these deposits over a geological timeframe of millions of years can ensue through subsidence of coastal sediments and during sea level change that results in either shorelines migrating inland marine transgression or seaward marine regression potentially burying or stranding earlier deposits or reworking them to form younger deposits refinements in remote sensing and geophysical techniques data processing sedimentology and computer aided interpretations provide effective economic and efficient methods for modeling coastal reconstructions and for exploring provinces and terrains prospective for heavy mineral sand deposits landscape topography analysis combined with geophysical methods that can resolve physical property contrasts between the shoreline sediments and underlying sequences are increasingly used in mineral exploration to locate and to reconstruct paleoshorelines and paleovalleys australia has modern and ancient beach placer deposits both of which show many similar geologic features the formation of these heavy mineral deposits provides one of the best examples of applying knowledge of modern systems e g the west and east coasts of australia as an analogue to interpret and understand the geology and form of ancient deposits e g the eucla and murray basins of southern australia this study provides descriptive and exploration models of australia s heavy mineral sand deposits formed in coastal environments which can be applied to similar settings worldwide

remote sensing evidence of lava ground ice interactions associated with the lost jim lava flow seward peninsula alaska thermokarst terrains develop when ice bearing permafrost melts and causes the overlying surface to subside or collapse this process occurs widely throughout arctic regions due to environmental and climatological factors but can also be induced by localized melting of ground ice by active lava flows the lost jim lava flow ljlf on the seward peninsula of alaska provides evidence of former lava ground ice interactions associated geomorphic features on the scale of meters to tens of meters were identified using satellite orthoimages and stereo derived digital terrain models the flow exhibits positive and mixed relief features including tumuli n 26 and shatter rings n 4 as well as negative relief features such as lava tube skylights n 100 and irregularly shaped topographic depressions n 1188 that are interpreted to include lava rise pits and lava induced thermokarst terrain along the margins of the flow there are also clusters of small peripheral pits that may be the products of meltwater or steam escape on mars we observed morphologically similar pits near lava flow margins in northeastern elysium planitia which suggests a common formation mechanism investigating the ljlf may therefore help to elucidate processes of lava ground ice interaction on both earth and mars

quiet ionospheric currents of the southern hemisphere derived from geomagnetic records a special selection of extremely quiet 1965 geomagnetic daily variation records from north america europe central asia and east asia was used to determine monthly spherical harmonic analysis coefficients representing the sq fields from these regions the coefficients permitted a separation of the external and internal contributions to the daily variations month by month behavior of the equivalent external current system and contours of the daily range of this current showed regional differences in amplitude and location of the equivalent ionospheric currents with seasonal change current foci locations reached 35 to 42 geomagnetic latitude in summer and 18 to 35 in winter with a regional dependence the largest daily range of external current was 14 6 104 a in north america 15 3 104 a in europe 13 7 104 a in central asia and 12 3 104 a in east asia continental differences in the behavior of the current seemed to be explained by the relative position of the geographic and geomagnetic poles with respect to these regions

mars a review and synthesis of general environments and geological settings of magma h2o interactions the advent of a global cryosphere likely occurred very early in the history of mars and much of the available water and related volatiles co 2 clathrates etc were sequestered within and below the cryosphere this means that magmatism plutonism and volcanism as a geological process throughout the history of mars cannot be fully understood without accounting for the interaction of magma and water and related species in both solid and liquid form we review and outline the probable configuration of water and ice deposits in the history of mars describe environments and modes of magma h 2o interaction and provide specific examples from the geological record of mars magma and water ice interactions have been interpreted to have formed 1 massive pyroclastic deposits 2 large scale ground collapse and chaotic terrain 3 major outflow channels 4 mega lahars dwarfing terrestrial examples 5 sub ice sheet eruptions and edifices 6 pseudocraters 7 landslides on volcanic edifice flanks and 8 hydrothermal sites the global nature of the cryosphere its longevity and the diversity of environments means that mars is an excellent laboratory for the study of magma h 2o interactions and the role of related volatile species

heavy mineral beach placers in southeastern australia their nature and genesis southeastern australia has been one of the world s most productive heavy mineral sand provinces concentrations of detrital rutile zircon ilmenite and minor monazite occur as beach placers and in dunes in high stand barriers of quaternary age along the present coast although individual mineral grains are of terrigeneous origin the heavy mineral deposits themselves are not linked to specific source rocks in the hinterland rather they arise under the action of waves during the building of coastal sand barriers a number of fractionating mechanisms that concentrate heavy minerals operate during marine transgressions and under highstand conditions to produce three different types of beach placers type a deposits occur along erosional discontinuities in leaky embayments or between barriers of different age here repeated storm reworking has produced beach face concentrations on drift aligned sectors of coast by a process termed littoral bypassing fractionation type b heavy mineral deposits are found in back barrier washover facies and sometimes as condensed sections at the rear of swash aligned barriers in coastal embayments these were produced by a process of transgressive barrier fractionation that reworked heavy minerals from shelves undergoing erosion during marine transgressions type c heavy mineral deposits occur in prograded barriers and represent episodic influxes of remobilized heavy mineral rich sand that originated elsewhere through the two fractionation mechanisms mentioned above necessary environmental conditions for these fractionating mechanisms to operate include low rates of clastic sediment supply and long periods of weathering and abrasion to create a mature heavy mineral suite an energetic swell wave climate driving large sand fluxes onshore and alongshore and changing sea levels especially marine transgressions that have the effect of moving heavy minerals from the shelf onto the present coast because of the last mentioned effect the mineral prospectivity for the southeastern australian continental shelf is not high

external sq currents in the india siberia region the sq current systems for quiet days of 1976 and 1977 were studied for observatories established near 76 degrees e longitude in the northern hemisphere a special sperical harmonic analysis technique was used to separate the internal and external contributions of the quiet field variations and to determine the equivalent external current contours responsible for the sq field variations on the sixth and twenty first of each month the average ratio of the external to internal spectral power was 6 7 in 1976 and 7 4 in 1977 focus positions for the india siberia region external sq current vortex near 22 degrees to 29 degrees were found to be at lower geomagnetic latitudes than for europe and north america the usual mid latitude vortex current reaching 11 0 to 13 2 times 10 sup 4 a in summertime disappeared completely during winter months in both the years the sq current position was affected clearly by the off spin axis position of the north geomagnetic pole throughout the 2 years the authors also found small current vorticies near 70 degrees to 80 degrees geomagnetic latitude which have been ascribed to auroral region activity on quiet days 19 refs 11 figs 1 tab

geochemical evolution of the northern plains of mars early hydrosphere carbonate development and present morphology it is likely that early in mars history abundant liquid water was available under a thick several bars carbon dioxide atmosphere this water could have formed an ocean located primarily in the lowlands of the northern hemisphere an equilibrium geochemical model of this ocean and its interactions with the atmosphere and regolith of mars was developed and the results of this model were used to discuss the evolution of the volatile budget of mars including the deposition of large carbonate beds on the northern plains differential solutional weathering of these carbonate beds may have caused the formation of some of the enigmatic features seen on the northern plains of mars such as the thumbprint terrain and enclosed depressions

paucity of candidate coastal constructional landforms along proposed shorelines on mars implications for a northern lowlands filling ocean abstract the case for an ocean having once occupied the northern lowlands of mars has largely been based indirectly on the debouching of the outflow channels into the lowlands and directly on erosional features along the margins of the lowlands interpreted to be the result of wave action two global shorelines were previously mapped from albedo variation embayment relationships and scarps interpreted as coastal cliffs however not since the early viking based studies has there been a focused assessment of the presence or absence of coastal constructional landforms such as barrier ridges and spits located on or near the mapped shorelines such constructional landforms are typically found in association with coastal erosional features on earth and therefore warrant a detailed search for their presence on mars all presently available themis vis and moc na images located on or near either of the two shorelines within the chryse planitia arabia terra region 10 to 44 n 300 to 0 e and the isidis planitia region 0 to 30 n 70 to 105 e were examined in search of any features that could reasonably be considered candidate coastal ridges additionally raw mola profiles were used in conjunction with a technique developed from differential global positioning system profiles across terrestrial paleo shorelines to search for coastal ridges throughout these same regions out of 447 themis vis and 735 moc na images examined only four candidates are observed that are plausibly interpreted as coastal ridges no candidate coastal ridges are observed in the mola profiles this overwhelming paucity of candidate features suggests one of five possible scenarios in terms of the existence of standing bodies of water within the martian lowlands 1 no ocean existed up to the level of either of the previously mapped shorelines 2 an ocean existed however wave action the primary agent responsible for construction of coastal landforms was minimal to non existent 3 an ocean existed but sediment input was not significant enough to form coastal deposits 4 an ocean existed but readily froze and over time sublimated and lastly 5 an ocean existed and coastal landforms were constructed but in the intervening time since their formation they have nearly all been eroded away

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

clustering within rootless cone groups on iceland and mars effect of nonrandom processes 1 this study aims at quantifying the spatial distribution of cones within rootless cone groups rcgs our data set consists of 1 seven icelandic rcgs identified through field investigations 2 seven candidate rcgs on mars identified through mars orbiter camera moc and thermal emission imaging system themis images and 3 four groups of impact craters on mars also identified through moc and themis images to determine if they can be remotely distinguished from the rcgs purely on the basis of their spatial distribution several independent statistical techniques are used including nearest neighbor analysis analysis of variance anova and linear alignment detection analysis our results indicate that the spatial distribution of each rcg is not random within a cone group cones preferentially form near existing cones the presence of at least one significant linear cone alignment in each rcg and strong linear alignments in some groups suggests that rootless cones form as the surface signature of preferred lava pathways an anova on mean nearest neighbor distances reveals the martian cone groups to be statistically indistinguishable from the icelandic rcgs supporting existing interpretations that they represent rootless cone groups a similar anova showed that the martian cone groups do not resemble the martian impact crater clusters studied the impact craters have significantly greater nearest neighbor distances and show no evidence of aggregation within a crater group

icelandic pseudocraters as analogs to some volcanic cones on mars pseudocraters are rootless vents formed by the interaction of lava flows with surface or near surface water this interaction can produce mild explosions and the accumulation of scoria and spatter into small constructs pseudocraters in several localities in iceland were examined in the field and compared to similar appearing features observed on mars the icelandic pseudocrater cones in this study range in size from 6 to 70 m in diameter have summit craters which range from 2 to 28 m in diameter many cones lack craters entirely and have flanks that are either concave up or convex up the size and spacing of icelandic pseudocraters might be a function of the availability of water in which larger closely spaced features result from efficient lava water interaction as suggested by the environments in which the features formed possible martian pseudocrater cones in amazonis planitia range in diameter from 30 to 180 m and have craters 12 to 80 m in diameter a numerical model for volcanic explosions was adapted to study the formation of pseudocraters under terrestrial and martian conditions the results suggest that explosions forming martian cones require significantly less water calculated masses are less by a factor of 4 to 16 than those forming icelandic pseudocraters despite their larger sizes this is attributed to the low gravity and atmospheric pressure in the mars environment and is consistent with the likely lower abundance of water which might be present as interstitial ice at shallow depths in the regolith locations of potential pseudocraters on mars at latitudes as low as 8 n imply the presence of crustal ice stores at the time of their formation

mars exploration rover candidate landing sites as viewed by themis the analysis of six landing sites that were candidates for the two nasa mars exploration rovers mer benefited from recently available image data from the thermal emission imaging spectrometer themis onboard the 2001 mars odyssey spacecraft the combination of daytime and nighttime thermal infrared images from themis supplemented by additional data sets has lead to new or expanded insights into the nature of each landing site in meridiani planum a layer of lighter toned higher thermal inertia material is observable just below the hematite bearing layer gusev crater displays a more complex stratigraphy than previously observed including an upper layer with lobate margins the highest inertia unit of southern isidis planitia is confined to topographic lows in the rim basin margin and does not appear to be due to highland material transported onto the basin floor the enigmatic ovoid blocky terrain on the floor of melas chasma displays higher thermal inertia than its surroundings an indication that it contains coarser or more indurated material than the adjacent aeolian bedforms the myriad channels of athabasca valles display distinctive thermal signatures despite the presence of a bright layer of dust covering the region the presence of alluvial fans produced from spur and gulley erosion of the walls of eos chasma demonstrates that mass movements have occurred following the canyon scouring floods

grid mapping the northern plains of mars using morphotype and distribution of ice related landforms to understand multiple ice rich deposits in utopia planitia this work in utopia planitia is the first continuous regional mapping of ice related landforms integrated into an effort to study the three main basins arcadia acidalia utopia planitiae in the northern plains the distribution and morphotypes of these landforms sharad detections and crater size frequency distribution measurements 50 m in diameter were used to understand the permafrost cryolithology and its past evolution in relation to climate in utopia planitia three assemblages of landforms were identified based on their spatial correlation and correlation with mola surface roughness along a strip from 30 n to 80 n at 30 38 n the assemblage is formed by km scale polygons high albedo mounds and thumbprint terrains this assemblage is associated with a lobate deposit of 30 m in thickness with a crater retention age of 1 ga at 38 47 n the assemblage is comprised of large scallops 100 m diameter polygons pits and mantled deposits this assemblage is correlated with a deposit of 80 m in thickness containing excess ice 50 85 by volume with a crater retention age of about 10 ma at 47 78 n the assemblage is composed of mantled deposits textured terrains and 30 m diameter polygons this assemblage is related to the ice rich debris covered latitude dependent mantle that has a crater retention age of about 1 5 ma utopia planitia appears to be a region of combined depositions of sediment and continuous cold climatic conditions that leaded to a complex distribution of ground ice

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

formation and evolution of the chaotic terrains by subsidence and magmatism hydraotes chaos mars the origin of the martian chaotic terrains is still uncertain and a variety of geologic scenarios have been proposed we provide topographic profiles of different chaos landscapes notably aureum and hydraotes chaos showing that an initial shallow ground subsidence occurred at the first step of the chaos formation we infer that the subsidence was caused by intrusion of a volcanic sill which could have produced consequent melting as well as release of ground water from disrupted aquifer signs of a volcanic activity are observed on the floor of hydraotes chaos a complex and deep depression located at the junction of three channels the volcanic activity is represented by small 0 5 to 1 5 km diameter rounded cones with summit pits the cone s size and morphology as well as the presence of possible surrounding lava flows suggest that they are primary volcanic cones similar to terrestrial cinder cones the identification of volcanic activity on the deepest chaos where the lower crustal thickness and the faults fractures system contributed to the magma rising reveals that magmatic activity proved by the cones and possibly help by structural activity has been a major factor in the formation of chaotic terrains

the evolution of coastal barrier systems a case study of the middle late pleistocene wilderness barriers south africa abstract barrier systems contain lengthy but complex records of long term environmental fluctuations the wilderness embayment south africa contains a system of shore parallel barriers reaching up to 200 m above modern sea level this study reports the results of chronological topographical both on and off shore sedimentological and micromorphological analyses within the wilderness embayment sixty one new luminescence ages from sixteen sites in unconsolidated dunes and three separate barriers are presented which when combined with previously published luminescence ages from the area provide a high resolution chronological framework for the emplacement and evolution of the barrier system the preserved barriers have been constructed within at least the last two glacial interglacial cycles with notable phases between 241 221 ka 159 143 ka 130 120 ka 92 87 ka and post 6 ka multiple phases of barrier construction occurred during sea level highstands with sediment deposition on each individual barrier occurring over at least two interglacials holocene evolution of the system sheds light on earlier events with dune preservation occurring only during early regression from the mid holocene highstand tectonic stability at wilderness allowed glacio eustatically formed shorelines to occupy similar positions on multiple occasions this in conjunction with a relatively humid climate and a well vegetated landscape enabled deflated sediment from beaches to form dunes which stacked upon each other to form an extensive and complex vertical accretionary sequence repeated erosion and recycling of pre existing barriers as well as barrier construction on what is currently the off shore platform during still stands in sea level regressional cycles when sea levels dropped below ca 50 m from the present day has added to the complexity of the preserved terrestrial barrier record the wilderness barrier system contrasts with barriers developed elsewhere in the world where higher rates of crustal uplift have allowed preservation of a more complete and more widely spaced palaeorecord this research also shows the utility of integrating off shore topography as revealed by bathymetry with terrestrial topographic data for the better understanding of the evolution of palaeo coastlines and the preserved dune record found on present day coastal plains local variation in the topography of the continental shelf at wilderness has generated spatial and temporal complexity within the sedimentary records of individual barriers as well as having a significant influence on preservation

the stratigraphy of the amenthes region mars time limits for the formation of fluvial volcanic and tectonic landforms abstract we present results of our morphologic and stratigraphic investigations in the amenthes region for which our observations suggest a complex spatial and temporal interrelation between volcanic and possibly water related processes we have produced a series of self consistent geological maps and a stratigraphic correlation chart that show the spatial and temporal distribution of volcanic fluvial and tectonic processes the amenthes region consists of a broad trough like topographic depression that has served as a path for the supply of materials from hesperia planum to isidis planitia it is most likely that hesperia planum and in particular the area north of hesperia planum including tinto vallis palos crater and the surrounding dissected highlands have acted as a source region for materials that were transported into the amenthes trough and farther into the isidis basin the amenthes trough as well as the graben of amenthes fossae were formed after the isidis impact in the noachian and represent likely the oldest features in the amenthes region dendritic valley networks that bear evidence for surface runoff have dissected the highlands adjacent to amenthes planum and within the tinto vallis and palos crater region before 3 7 ga the ridged volcanic plains located near the palos crater and tinto vallis region within amenthes planum as well as within the isidis transitional plains were formed between 3 5 and 3 2 ga and represent the volcanic activity which resulted in the flooding of the amenthes trough the sinuous channel of tinto vallis was formed in the hesperian 3 5 ga and shows characteristics which are consistent with both ground water sapping and igneous processes the palos crater outflow channel was formed nearly at the same time as tinto vallis between 3 5 ga and 3 2 ga and postdates the volcanic flooding of the amenthes trough in the hesperian small valleys 3 4 2 8 ga incised into the ridged plains of amenthes planum appear also within the transitional plains located between the amenthes plains and the isidis interior plains our model ages show that tinto vallis the palos crater outflow channel as well as the small valleys are unlikely formed at the same time and by the same processes as the dendritic valley networks and represent an episode that clearly postdates the volcanic activity

mineral sands occurrences in the murray basin southeastern australia the murray basin in southeastern australia is proving to be a major mineral sand province that eventually will replace australia s east and west coasts in production of rutile zircon and ilmenite concentrations of relatively coarse grained heavy mineral occur as beach placers in the pliocene loxton parilla sands in the upper part of the murray basin sequence these formed as 400 km long barrier complexes in the murravian gulf under the action of long period ocean swell waves we think the main source of barrier sand at least initially was from erosion of miocene sands on the bed of the murravian gulf progradation was a response to sea level fluctuations linked to milankovitch climatic cycles in the pliocene in most areas the resulting 400 km wide barrier strand plain is now overlain by fluvial aeolian and lacustrine deposits typically the heavy mineral deposits are ilmenite rich with 30 to 40 percent rutile and zircon they occur as single or as multiple stacked strandline deposits are often more than 10 m thick have mineral grades that exceed 20 percent in places are several hundred meters wide and 10 to 25 km long some contain up to several million tonnes of heavy mineral the rutile and zircon are comparable in grain size and quality to minerals traditionally mined in australia many of the deposits are associated with topographic ridges the neckarboo and iona ridges are the best known that appear to be fault bounded blocks deposits of major commercial significance found so far contain a total of over 12 million tonnes mt of rutile zircon and ilmenite the total coarse grained mineral sand resources in the murray basin are conservatively estimated to be over 50 mt the distribution of mineral sands in the murray basin seems to be associated with two aspects of the region s geology and geomorphology 1 a zone bordering the central part of the basin where the pliocene barriers were derived from underlying miocene sands that probably already contained some mineral concentrations and 2 growth faulting with deposits preferentially occurring on upfaulted blocks especially in the zone defined by 1 above we speculate that localized uplift during the formation of the loxton parilla barriers was sufficient to modify coastal processes on uplifted blocks so as to increase the rate of alongshore sediment bypass compared to nearby areas this phenomenon has been simulated in computer modeling where the barrier sands were already enriched in heavy minerals winnowing by storm waves formed beach placers on the uplifted fault blocks based on criteria 1 and 2 the prospective areas of the murray basin account for 80 percent of the beach placers found to date

pliocene sedimentation in a shallow cool water estuarine gulf murray basin south australia the pliocene norwest bend formation is a well preserved succession of terrestrial and shallow marine deposits in the murray basin south australia sediments in this unit consist of two discrete terrigenous clastic rich decametre scale sequences or informal members which record episodes of marine incursion during the early and late pliocene respectively the base of each sequence is a transgressive lag and or strandline deposit that is transitional upwards into a highstand subtidal terrigenous clastic and cool water carbonate sediment accumulation the top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea level fell and terrestrial environments prograded basinward sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy differences in sedimentary style between these two sequences however reflect a major climatic change that took place in southern australia during the mid pliocene the lower quartzose sand member is formed of siliciclastic sediment derived from prolonged deep subaerial weathering and contains a bivalve dominated cool temperate open marine mollusc assemblage these sediments accumulated under an equitable relatively warm humid climate the murray basin during this time because of high fluvial discharge was a salt wedge estuary with typical estuarine circulation in contrast the upper oyster rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments strandline deposits contain a warm temperate skeletal assemblage contemporaneous aeolian sediments accumulated under warm semi arid climatic conditions well developed ferricrete silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern australia today highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed these pliocene sediments support the notion that mollusc rich facies are the signature of cool water carbonate accumulations in inboard neritic environments unlike bryozoans that dominate the outer parts of cenozoic cool water carbonate shelves molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates

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

utopia basin mars characterization of topography and morphology and assessment of the origin and evolution of basin internal structure recently obtained mars orbiter laser altimeter mola topography has permitted a new assessment of the morphology structure and history of utopia planitia the new topographic data convincingly demonstrate that the utopia region is an impact basin as originally proposed by mcgill 1989 whose major topographic expression is a circular 1 3 km deep depression 3200 km in diameter utopia basin is the largest easily recognizable impact structure in the northern hemisphere of mars and is the only portion of the northern lowlands that exhibits a distinct large scale impact signature its presence there and its ancient age verify that a significant part of the northern lowlands dates back to the noachian period using slope maps derived from gridded topography we have mapped a series of linear slope anomalies within the basin and have analyzed their origin these features can be classified into two groups one oriented dominantly radial to the basin and the other oriented dominantly circumferential the circumferential features are tens of kilometers wide and hundreds of kilometers long and appear to remain relatively constant with respect to elevation we explore end member hypotheses 1 that the features formed by the direct action of water ice or 2 that they are tectonic wrinkle ridges we interpret the majority of these features to be due to tectonic deformation primarily wrinkle ridge formation modified by later sedimentation associated with the emplacement of the outflow channels and the formation of the vastitas borealis formation on the basis of the characteristics of these features and their association with polygonal terrain thumbprint terrain smoothness of units and evidence of sedimentary deposits we find that our results support earlier hypotheses proposing that a significant volume of water occupied utopia basin during the late hesperian period of outflow channel formation utopia basin differs significantly in depth and degradation state from the deeper and fresher appearing hellas basin although the two are both noachian in age a significant part of this difference seems reasonably interpreted to be the result of the extensive sedimentary and volcanic infilling history of the northern lowlands

geotraverse from xanthe terra to chryse planitia viking 1 lander region mars high resolution 1 500 000 scale geologic mapping of a 300 km wide and 1500 km long strip or geotraverse across the transition from the xanthe terra cratered highlands to the chryse planitia lowlands encompasses an area on the margin of the chryse basin unaffected by outflow channels it thus characterizes the transition where it has been relatively unmodified by erosion and the stratigraphy of pre outflow units is well preserved two types of highland lowland boundary are identified 1 a topographic boundary and 2 a geologic morphologic boundary the topographic boundary occurs well within the cratered highlands and separates a lower standing surface with characteristics transitional to cratered highlands from the true highland surface of xanthe terra the lower transitional highland surface or transition zone is partially inundated by plains forming materials interpreted to be plains type lava flows of late noachian early hesperian age similar to later basin fill material forming hesperian aged lowland ridged plains the geologic boundary between this transitional surface and ridged lowland plains surface is identified with the traditional highland lowland boundary as mapped in previous studies mapping in this study identifies a moat like region between this geologic boundary and the basin interior is filled with an easily eroded material erosion of the moat filling deposit along the outer margins of the chryse basin accounts for the streamlined tables formed during outflow channeling throughout the margins of chryse planitia the geology of the central basin interior where the viking 1 lander is located is consistent with the presence of fluvial sediments derived from both the adjacent highlands and remobilized from the marginal moat filling unit and deposited near the termini of the maja and kasei valles outflow channels because the plains forming lavas overlie much of the proximal portions of the highlands and moat filling sediments ring the margins of the basin materials eroded from the transition zone and deposited toward the basin interior by later outflow channels may be similar to interior plains lavas and marginal moat filling deposits if the transitional highland surface is typical of the basin elsewhere true highland rocks are likely to be a small component of any outflow channel sediments even in settings near the basin margin rock populations and sediments at the proposed mars pathfinder site located near the geologic boundary further east could contain a significant portion of materials typical of lowlands in addition to some highland materials

martian perched craters and large ejecta volume evidence for episodes of deflation in the northern lowlands the northern lowland plains such as those found in acidalia and utopia planitia have high percentages of impact craters with fluidized ejecta in both regions the analysis of crater geometry from mars orbiter laser altimeter mola data has revealed large ejecta volumes some exceeding the volume of excavation moreover some of the crater cavities and fluidized ejecta blankets of these craters are topographically perched above the surrounding plains these perched craters are concentrated between 40 and 70 n in the northern plains the atypical high volumes of the ejecta and the perched craters suggest that the northern lowlands have experienced one or more episodes of resurfacing that involved deposition and erosion the removal of material most likely caused by the sublimation of ice in the materials and their subsequent erosion and transport by the wind is more rapid on the plains than on the ejecta blankets the thermal inertia difference between the ejecta and the surrounding plains suggests that ejecta characterized by a lower thermal inertia protect the underneath terrain from sublimation this results in a decreased elevation of the plains relative to the ejecta blankets sublimation and eolian erosion can be particularly high during periods of high obliquity

the upper mantle conductivity analysis method using observatory records of the geomagnetic field the electrical conductivity of the earth s upper mantle can be inferred from geomagnetic quiet day sq variations recorded at the world s observatories using the coefficients of a spherical harmonic analysis sha that separate the external source and internal induced parts of the surface field the conductivity profile determined from such an analysis can be sensitive to special characteristics of the quiet field itself as well as the separation techniques employed this review of the sq analysis features critical to a conductivity derivation is pictorially presented along with the equations for application of theschmucker 1970 technique to thesha coefficients for a conductivity determination three examples illustrate the use of these equations with differentsq models

rootless cones on mars indicating the presence of shallow equatorial ground ice in recent times high resolution mars orbiter camera moc images have revealed the existence of clusters of small cones in the cerberus plains marte valles and amazonis planitia mars these cones are similar in both morphology and planar dimensions to the larger of icelandic rootless cones which form due to explosive interactions between surficial lavas and near surface groundwater impact crater size frequency relationships indicate that surfaces upon which the cones sit are no older than 10 ma if martian cones form in the same manner as terrestrial rootless cones then equatorial ground ice or ground water must have been present near the surface in geologically recent times

geology and mer target site characteristics along the southern rim of isidis planitia mars 1 the southern rim of the isidis basin contains one of the highest densities of valley networks several restricted paleolake basins and the stratigraphically lowest oldest terrain on mars geologic mapping in viking mgs moc and mola data odyssey themis data and other multispectral data products supports the presence of extensive fans of debris and sediments deposited along the inner rim of the isidis basin where large valleys enter the lowlands additional processes subsequent to the period of intense fluvial activity including mass flow analogous to some glacial processes have contributed to the materials accumulated on the margins of the isidis basin these have occurred along preexisting channels and valleys at the termini of major channels where they enter the plains along the highland lowland boundary if the abundant valley networks in highland terrains are the result of runoff accompanied by saturated groundwater flow as has been suggested in previous studies of ancient fluvial highland terrains then the extreme age and abundance of early valley networks in the libya montes highland rocks should have resulted in deposition of materials that record evidence for the long term presence of water in the form of aqueous alteration of polycrystalline constituents the material deposited along the basin margin is likely to consist of ancient altered highland rocks in several physical states weathered rounded and angular exposing both weathered and altered surfaces and exposures of alteration profiles in fractured faces and unweathered material from rock interiors debris fans shed off the southern rim of isidis planitia should contain materials that have experienced possible saturated groundwater flow residence within paleolake basins and derivative materials deposited during the most fluvially intensive part of martian geologic history many of these materials have also been reworked by ice related processes in situ measurements of the ancient crustal materials in the form of rocks within the debris fans and the weathered condition of the rocky material are potential sources for mineralogical evidence of climatic conditions in earliest martian geologic history the absence of alteration within rocks would on the other hand support the hypothesis that fluvial runoff during the earliest history of mars was geologically brief rather than long term and that long term saturated groundwater flow was not present determination of the presence or absence of alteration would have corresponding implications for hypotheses requiring the long term presence of aqueous solutions i e complex organic compounds and life a proposed mer site along the margin addresses realistic field science objectives of the mars exploration rover mission and the current goals of the mars exploration program in situ measurements may be important in deriving estimates of the longevity and intensity of past wetter climates

higher order neighbor analysis of the tartarus colles cone groups mars the application of geographical indices to the understanding of cone pattern evolution cone fields of ambivalent origin exist in the elysium amazonis cerberus isidis acidalia and cydonia regions of mars considerable interest exists in regard to their location and origin as their occurrence in many instances is most likely associated with near surface ground ice the presence of which has consequences for past and present climate astrobiological activity and future exploration this research has outlined an understanding of both spatial and geomorphic processes of cone development for a region within the tartarus colles mars as well as the manner in which spatial statistical indices can be affected by modification to the areal unit of study this study found that cone groups for the region of the tartarus colles are completely spatially random csr across all distances extending to their sixth order neighbor however significant statistical indices of aggregation were found for groups where post emplacement erosional modification may have occurred by solifluction like mechanisms or magmatic incursion into or over frozen ground such circumstances imply that r indices reflect both the underlying spatial and geologic processes of cone formation and also an overprint of erosional modification of the cone field within a glacial or periglacial setting in this instance the comparison of spatial indices can therefore offer a viewpoint from which geomorphic change can be recognized and quantitatively evaluated for cone fields

an introduction to quiet daily geomagnetic fields on days that are quiet with respect to solar terrestrial activity phenomena the geomagnetic field has variations tens of gamma in size with major spectral components at about 24 12 8 and 6 hr in period these quiet daily field variations are primarily due to the dynamo currents flowing in the e region of the earth s ionosphere are driven by the global thermotidal wind systems and are dependent upon the local tensor conductivity and main geomagnetic field vector the highlights of the behavior and interpretation of these quiet field changes from their discovery in 1634 until the present are discussed as an introduction to the special journal issue on quiet daily geomagnetic fields

alteration of detrital fe ti oxides in sedimentary rocks scanning electron microscope study has revealed that in proterozoic sandstones shales and carbonate rocks of the visingso group in southern sweden detrital fe ti oxides have undergone alteration by dissolution and or replacement mainly by titanium oxides hematite reddish rocks or pyrite greenish sandstones shales and carbonate rocks the titanium oxides occur as either poorly crystalline masses cryptocrystalline aggregates or discrete euhedral crystals of anatase brookite and rutile that attain a variety of crystal habits microprobe analyses have shown that the alteration of ilmenite occurs through several intermediate phases each successively enriched in titanium and depleted in iron to an almost pure form of tio 2 some of the iron and titanium which is released during alteration of the fe ti oxides is incorporated in associated clay minerals

spatial distribution of putative water related features in southern acidalia cydonia mensae mars abstract many putative water related features exist in the northern lowlands of mars these features may provide clues to the abundance and timing of water or ice that existed there in the past the cydonia mensae and southern acidalia area was chosen as the study area owing to the abundance of two of these features giant polygons and pitted cones in addition a section of the deuteronilus shoreline is located there the abundance and close proximity of the features makes this area an excellent place to study the spatial relationships between these landforms as well as the morphological characteristics of pitted cones the features were mapped into a gis for spatial analyses the highest densities of pitted cones and giant polygons are adjacent but distinctly separated by a knobby ridge that is surrounded by the deuteronilus putative shoreline pitted cones were measured and examined to determine if a classification by morphology is possible but the results were inconclusive statistical tests on pit to cone diameter ratios and tests of surface temperatures of cone material suggest but do not verify a single cone origin the various shapes sizes and putative ages of pitted cones may be attributed to temporal variation in emplacement and spatial variation in material properties among the possible scenarios put forth for pitted cone genesis on mars two are likely candidates in cydonia mensae 1 the sublimation of a cold based glacier and 2 a buried lens of methane and or co2 clathrates

explosive lava water interactions in elysium planitia mars geologic and thermodynamic constraints on the formation of the tartarus colles cone groups 1 volcanic rootless constructs vrcs are the products of explosive lava water interactions vrcs are significant because they imply the presence of active lava and an underlying aqueous phase e g groundwater or ice at the time of their formation combined mapping of vrc locations age dating of their host lava surfaces and thermodynamic modeling of lava substrate interactions can therefore constrain where and when water has been present in volcanic regions this information is valuable for identifying fossil hydrothermal systems and determining relationships between climate near surface water abundance and the potential development of habitable niches on mars we examined the western tartarus colles region 25 27 n 170 171 e in northeastern elysium planitia mars and identified 167 vrc groups with a total area of 2000 km2 these vrcs preferentially occur where lava is 60 m thick crater size frequency relationships suggest the vrcs formed during the late to middle amazonian modeling results suggest that at the time of vrc formation near surface substrate was partially desiccated but that the depth to the midlatitude ice table was 42 m this ground ice stability zone is consistent with climate models that predict intermediate obliquity 35 between 75 and 250 ma with obliquity excursions descending to 25 32 for lava thicknesses ranging from 30 to 60 m and ground ice fractions ranging from 0 1 to 0 3 an ice volume of 4 23 km3 could have been melted and or vaporized by the time the lava solidified and the associated hydrothermal systems could have retained temperatures 273 k for up to 1300 years

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

explosive lava water interactions ii self organization processes among volcanic rootless eruption sites in the 1783 1784 laki lava flow iceland we have applied quantitative geospatial analyses to rootless eruption sites in the hnuta and hrossatungur groups of the 1783 1784 laki lava flow to establish how patterns of spatial distribution can be used to obtain information about rootless cone emplacement processes and paleo environments this study utilizes sample size dependent nearest neighbor nn statistics and voronoi tessellations to quantify the spatial distribution of rootless eruption sites and validate the use of statistical nn analysis as a remote sensing tool our results show that rootless eruption sites cluster in environments with abundant lava and water resources but competition for limited groundwater in these clusters can cause rootless eruption sites to develop repelled distributions this pattern of self organization can be interpreted within the context of resource availability and depletion topography tends to concentrate lava fuel and water coolant within topographic lows thereby promoting explosive lava water interactions in these regions given an excess supply of lava within broad sheet lobes rootless eruption sites withdraw groundwater from their surroundings until there is insufficient water to maintain analogs to explosive molten fuel coolant interactions rootless eruption sites may be modeled as a network of water extraction wells that draw down the water table in their vicinity rootless eruptions at locations with insufficient groundwater may either fail to initiate or terminate before explosive activity has ceased at nearby locations with a greater supply of water thus imparting a repelled distribution to observed rootless eruption sites

spectral evidence of volcanic cryptodomes on the northern plains of mars abstract the composition and detailed morphology of dome shaped features located in western arcadia planitia and just west of utopia planitia were examined in this study utilizing data from mars reconnaissance orbiter and mars odyssey sensors the domes have diameters averaging 1 5 km and heights averaging 160 m and are generally dark toned although some are lighter toned or have split dark and light toned surfaces the domes are surrounded by annular deposits comprising with increasing distance from the domes dark toned aprons light toned aureoles and dark toned aureoles compact reconnaissance imaging spectrometer for mars crism data over several areas in the western arcadia region show that spectra from the flanks of several domes have 1 and 2 m absorption features consistent with the presence of olivine and a high ca pyroxene nominally augite modified gaussian model mgm analysis of these spectra indicates fe rich olivine compositions the tops of domes and the aprons surrounding many domes have negative sloping flat spectra in the near infrared which is consistent with tachylite rich glassy compositions high resolution imaging science experiment hirise images over several domes indicate that relatively high thermal inertia values associated with the tops of domes can be attributed to boulder strewn surfaces hirise images also reveal that light toned aureoles around domes consist of crenulated ground resembling brain terrain textures previously described for ice rich concentric crater fill elsewhere on the northern plains the plains surrounding the domes also display lineations that are interpreted to be lava channels or tubes the combination of volcanic and ice related features are consistent with the domes having formed as cryptodomes in the near sub surface we suggest that the domes could be basaltic in composition if the magmas were degassed and or highly crystallized and thus more viscous than typical basaltic magmas the intrusion of these magmas into an ice rich horizon would have produced a pervasively jointed chilled margin on the domes which once the domes were exposed would have mechanically weathered to form the dark aprons the domes could have served as local centers for ice accumulation during periods of high orbital obliquity which ultimately would have led to the formation of the brain terrain surrounding the features the domes represent late stage volcanic products on the northern plains of mars and associated features provide more evidence for the role that ice accumulation and modification has played in recent martian history

candidate subglacial volcanoes in the south polar region of mars morphology morphometry and eruption conditions 1 a number of isolated mountains mapped in the south polar region of mars are documented using mars global surveyor mgs mars orbiter laser altimeter mola and mars orbiter camera moc data these mountains have average separation distances of 175 km they are typically 30 40 km in diameter and 1000 1500 m high and their bases fall near an elevation of 1200 m a significant number of the population are located on or very close to a 660 km long line extending toward the south pole the summits of a number of these mountains have unusual shapes flat topped flat topped with a cone and large summit craters relative to the summit diameter sinuous channels are found in association with the margins of several of the mountains several modes of origin are considered for these mountains including impact tectonic and volcanic these mountains occur in intimate association with the hesperian aged dorsa argentea formation a unit containing features and structures interpreted to be related to a thick areally extensive ice sheet on the basis of these observations and analyses it is concluded that the most plausible origin for these mountains is volcanic and that they represent extrusion of lava from vents many of which lay underneath an ice sheet the unusual shape of many of the mountains is consistent with construction of a volcanic edifice underneath an ice sheet and melting of adjacent ice rich material sometimes forming drainage channels the topography of these mountains suggests that the ice sheet averaged at least 1 4 km thick at the time of eruption these features appear to be associated with early hesperian aged ridged plains hr

a unique volcanic field in tharsis mars pyroclastic cones as evidence for explosive eruptions based on theoretical grounds explosive basaltic volcanism should be common on mars yet the available morphological evidence is sparse we test this hypothesis by investigating a unique unnamed volcanic field north of the shield volcanoes biblis patera and ulysses patera on mars where we observe several small conical edifices and associated lava flows twenty nine volcanic cones are identified and the morphometry of many of these edifices is determined using established morphometric parameters such as basal width crater width height slope and their respective ratios their morphology morphometry and a comparison to terrestrial analogues suggest that they are martian equivalents of terrestrial pyroclastic cones the most common volcanoes on earth the cones are tentatively interpreted as monogenetic volcanoes according to absolute model age determinations they formed in the amazonian period our results indicate that these pyroclastic cones were formed by explosive activity the cone field is superposed on an old elevated window of fractured crust which survived flooding by younger lava flows it seems possible that a more explosive eruption style was common in the past and that wide spread effusive plain style volcanism in the late amazonian has buried much of its morphological evidence in tharsis

sedimentary history and mass flow structures of chryse and acidalia planitiae mars geologic mapping and crater counting in chryse and acidalia planitiae cap reveal five major sedimentary deposits of hesperian to early amazonian age including 1 a mass flow deposited during the early hesperian near deuteronilus mensae northeast of the map region that may have resulted from the carving of kasei valles 3000 km southwest of the exposed part of the deposit 2 knobby plains material consisting of channel likely from simud and tiu valles and possibly ares and shalbatana valles and mass wasting deposits in central and eastern cap 3 material largely from maja and ares valles emplaced in at least western and southern cap outcrops in southern chryse planitia developed thermokarst 4 a thin mass flow covering much of southern chryse planitia that emanated from simud and tiu valles and 5 a thick extensive perhaps 3500 km across mass flow deposit in central and northern cap derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature various associated landforms appear to be consistent with the mass flow interpretations including lobate and linear scarps along deposit edges fractures related to desiccation of thick sediments troughs and ridges near the edges of the deposit indicative of secondary mass movement and deformation pitted domes and fissure fed flows possibly formed by sedimentary mud eruptions and longitudinal channel grooves perhaps formed by roller vortices no convincing evidence for paleoshorelines or stagnant ice sheets is found in cap these findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow channel dissection in cap elsewhere in the northern plains similar landforms are prevalent the mass flow interpretation does not require either multiple episodes of extraordinarily high water discharge rates achieved by freeing huge volumes of water from the crust repetitive recycling of immense volumes of water into highland aquifers at the heads of chryse channels or profound climate change mars pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of simud and tiu valles

origin of small pits in martian impact craters we propose a numerical model for the formation of the closely spaced pits found in the thin ejecta related deposits superposed on the floors interior terrace blocks and near rim ejecta blankets of well preserved martian impact craters our model predicts the explosive degassing of water from this pitted material which is assumed to originally be water bearing impact melt rich breccia at the time of deposition this process is analogous to what occurred in the fall out suevite deposits at the ries impact structure in germany at ries impact heating of water bearing target material resulted in the rapid degassing of its water and other volatiles the martian environment plays an important role in enhancing the effects of this degassing by increasing the flow speed of the escaping gas the high flow rate of gas through particulate materials such as suevite tends to quickly form segregation channels or vent pipes similar to those found in the ries deposits these pipes act as conduits for the efficient high speed escape of the gas and small clasts that it entrains escaping gas and entrained clasts abraded and eroded the conduit walls flaring them to form pits above a network of pipes

erosion sedimentation and pedogenesis in a polygenetic oxisol sequence in minas gerais brazil the geomorphic evolution of the south eastern brazilian landscape is attributed to climatic changes coupled with tectonic activity soils developed on the resulting surfaces are mainly deep polygenetic oxisols the combination of stable landscapes with continuously exposed soils and neo cenozoic graben zones episodically filled with sediments that may have undergone soil formation offers the possibility to unravel the history of the soils that are found at the present day surface soil sediment sequences in the southern part of the state of minas gerais brazil were investigated by micromorphology and mineralogy in order to understand the genesis of the soils erosion profile thinning weathering biological activity clay accumulation and iron translocation are the main soil forming processes imprinted in the various pedosedimentary layers strong weathering is shown by dissolution of quartz and weathering of ilmenite bioturbation is ubiquitous even in older and deeper buried layers clay accumulation is observed as illuviation and precipitation features which were micromorphologically differentiated accumulation and movement of iron are represented by gley and pseudogley features related to groundwater and surface water saturation processes these features and the layering of sediments and soils play key roles in understanding the evolutionary phases undergone by the soils and sediments as main soil formation episodes the graben fillings show two phases of clay formation and illuviation separated by a phase of ferralitization interrupted by various episodes of erosion the whole material was eventually overprinted by a phase of ferralitization and plinthite formation apart from water saturation these processes also appear to have acted on the soils of the stable areas not affected by tectonic activity but overprinting and erosion prevents recognition of the separate evolutionary phases

shoreline reconstruction since the middle holocene in the vicinity of the ancient city of apollonia albania seman and vjosa deltas abstract a geomorphological map was constructed based on satellite imagery of the recent geomorphological evolution of the delta of the seman and the vjosa rivers albania results of the analysis of data collected from unpublished geological profiles carried out by russian and albanian geologists indicate that concentrations of heavy minerals are clearly correlated with palaeo shorelines particularly in six boreholes drilled in the vicinity of the ancient city of apollonia 7th century bc 7th century ad study was mainly based on sedimentological pollen and diatom analysis about twenty samples of wood or peat debris have been 14c dated ams all between 3050 50 bp and 340 50 bp based on this evidence a new palaeogeographic reconstruction of the shoreline over the last 3500 years is proposed two thirds of the deltaic progradation occurred over the last 500 years as a hypothesis climatic fluctuations such as the little ice age and socioeconomic fluctuations could play a major role in the acceleration of the process in spite of an important neotectonic subsidence effect

rootless cones on mars a consequence of lava ground ice interaction fields of small cratered cones on mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow melting and vaporization of the ice and subsequent explosive expansion of the vapour act to excavate the lava and construct a rootless cone around the explosion site similar features are found in iceland where flowing lava encountered water saturated substrates the martian cones have basal diameters of c 30 1000 m and are located predominantly in the northern volcanic plains high resolution mars orbiter camera images offer significant improvements over viking data for interpretation of cone origins a new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features this is consistent with the likely low availability of water ice in the martian regolith the scarcity of impact craters on many of the host lava flows indicates very young ages suggesting that ground ice was present as recently as less than 10 l00 ma and may persist today rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on mars which is of key significance in understanding the evolution of the martian climate the location of water in liquid or solid form is of great importance to future robotic and human exploration strategies and to the search for extraterrestrial life

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

explosive lava water interactions i architecture and emplacement chronology of volcanic rootless cone groups in the 1783 1784 laki lava flow iceland to determine the relationships between rootless cone emplacement mechanisms morphology and spatial distribution we mapped the hnuta and hrossatungur groups of the 1783 1784 laki lava flow in iceland we based our facies maps on differential global positioning system dgps measurements photogeological interpretations and supporting field observations the study area covers 2 77 km2 and includes 2216 explosion sites to establish the timing of rootless cone formation we incorporated tephrochronological constraints from eighty eight stratigraphic sections and determined that the hnuta and hrossatungur groups are composite structures formed by the emplacement of six geographically and chronologically discrete domains rootless eruptions initiated in domain 1 on the first day of the laki eruption june 8 1783 and lasted 1 2 days the second episode of rootless activity began in domain 2 on june 11 and lasted 1 3 days the four domains of the hrossatungur group dominantly formed after june 14 and exhibit a complex emplacement sequence that reflects interactions between the laki lava contemporaneously emplaced rootless cones and an existing topographic ridge in the study area we identify three distinct rootless cone archetypes i e recurring morphological forms that are related to tube channel and broad sheet lobe fed eruptions we assert that emplacement of lava above compressible substrates e g unconsolidated sediments may trigger rootless eruptions by causing subsidence induced flexure and failure of the basal crust thereby allowing molten lava fuel to come into direct contact with groundwater coolant and initiating analogs to explosive molten fuel coolant interactions mfcis

lava flows on mars analysis of small surface features and comparisons with terrestrial analogs small scale surface features on lava flows provide information on the eruption parameters and the volcanic history of the flows in which they occur high resolution images of four sites on mars reveal lava flows with a different type or combination of features including pressure ridges tumuli festoon ridges and ring ridges pressure ridges tumuli and pressure plateaus are spaced irregularly and tend to be oriented parallel to flow they are formed by inflation of small flow lobes and are indicative of compound flows emplaced by sporadic eruptions with low effusion rates festoon ridges are oriented transverse to flow direction mimic the flow margin and have a regular spacing using a model by fink and fletcher 1978 and fink 1980 a interior viscosity values of approximately 108 pa s were calculated for festoon ridges tens to hundreds of meters apart and a few meters high on two basalt flows in iceland and a flow on mars this viscosity is comparable to results from similar studies of more silicic flows and suggests that high viscosities are necessary to form large festoon ridges by analogy to the icelandic flows martian flows containing festoon ridges are considered to be large single unit basalt flows emplaced through flood style eruptions high viscosity of the basaltic flows may result from cooling a high crystal content or low effusion temperatures disruption of the surface of some of these large sheet flows possibly by lava water interaction is suggested by the presence of ring ridges and rugged terrain consisting of mesa like mounds and channel like troughs

behavior of the quiet day ionospheric current system in the european region the ionospheric current system for magnetic quiet days deduced from geomagnetic field daily variations taken throughout europe at sunspot minimum has been studied special attention was paid to the selection of the representative quiet days showing the inadequacy of relying on the mean of the five international quiet days per month we used the technique of spherical cap harmonic analysis to separate the external and internal parts of the field variation from which the derivation of the equivalent current functions is straightforward this method provides a motion picture representation of the sq system through the screen formed by the spherical cap allowing the study of continuous variations with universal time detailed features of the current contours can be represented with such a regional analysis we found a strong day to day variability of the focus position along with some complexities that differ from the standard sq current behavior the average monthly or seasonal patterns are therefore averages of heterogeneous behaviors in many occasions possible explanations to these complex structures are considered

modeling tsunami propagation and the emplacement of thumbprint terrain in an early mars ocean the identification of lobate debris deposits in arabia terra along the proposed paleoshoreline of a former northern ocean has renewed questions about the existence and stability of ocean sized body of water in the early geologic history of mars the potential occurrence of impact generated tsunamis in a northern ocean was investigated by comparing the geomorphologic characteristics of the martian deposits with the predictions of well validated terrestrial models scaled to mars of tsunami wave height propagation direction runup elevation and distance for three potential sea levels our modeling suggests several potential impact craters 30 50 km in diameter as the source of the tsunami events within the complex topography of flat floored valleys and plateaus along the dichotomy boundary the interference of the multiple reflected and refracted waves that are observed in the simulation may explain the origin of the arcuate pattern that characterizes the thumbprint terrain

hydrovolcanic features on mars preliminary observations from the first mars year of hirise imaging abstract we provide an overview of features indicative of the interaction between water and lava and or magma on mars as seen by the high resolution imaging science experiment hirise camera during the primary science phase of the mars reconnaissance orbiter mro mission the ability to confidently resolve meter scale features from orbit has been extremely useful in the study of the most pristine examples in particular hirise has allowed the documentation of previously undescribed features associated with phreatovolcanic cones formed by the interaction of lava and groundwater on rapidly emplaced flood lavas these include moats and wakes that indicate that the lava crust was thin and mobile respectively jaeger w l keszthelyi l p mcewen a s dundas c m russel p s 2007 science 317 1709 1711 hirise has also discovered entablature style jointing in lavas that is indicative of water cooling milazzo m p keszthelyi l p jaeger w l rosiek m mattson s verba c beyer r a geissler p e mcewen a s and the hirise team 2009 geology 37 171 174 other observations strongly support the idea of extensive volcanic mudflows lahars evidence for other forms of hydrovolcanism including glaciovolcanic interactions is more equivocal this is largely because most older and high latitude terrains have been extensively modified masking any earlier 1 10 m scale features much like terrestrial fieldwork the prerequisite for making full use of hirise s capabilities is finding good outcrops