limnologic analysis of gusev crater paleolake mars abstract the survey of the hydrogeologic system formed by gusev crater and ma adim vallis aeolis subquadrangle of mars points out evidence for the existence of an ice covered lake in gusev crater a first lake was formed by the drainage of the aquifer in the region surrounding gusev before the entry of ma adim vallis in the crater the existence of a former lake in gusev is deduced from the morphology of the ma adim delta its comparison with terrestrial antarctic analogs argues for the presence of an ice covered lake in gusev at the time that the southern part of the crater s rampart was breached by ma adim first release and for a subice lacustrine construction of the valley s delta our survey shows that ma adim vallis may have entered gusev crater as late as late hesperian early amazonian as part of a second lake episode the relationship between the variation of the gusev lake water level the volume of the lake and the surface of the lake bed is established by our bathymetric model the elevation of the former lake is deduced from the elevation of the mesa like structures in the delta of ma adim vallis furthermore the correlation of the crater frequency of gusev rampart with mars stratigraphic age shows that lakes may have occupied gusev crater over a period of time covering 2 gyrs from the formation of the crater to the last episode of water release from ma adim vallis though it is most likely that the lake was episodical the recurrence of abundant water in gusev crater makes this site a high priority for missions either for martian resource exploration or for the search of life

venusian channels and valleys distribution and volcanological implications abstract nearly complete image coverage of venus by magellan enabled us to map various venusian channel and valley landforms and to examine their associations with other geological units global mapping reveals a nonrandom distribution the highest total concentration is in the equatorial regions characterized by highlands rift and fracture zones and associated volcanic features many channels associated with flow deposits are similar to typical terrestrial lava drainage channels they are observed to be associated with a wide range of volcanic edifices such as coronae shield volcanoes and rift and fracture zones one type of channel similar morphologically to lunar sinuous rilles is classified as a venusian sinuous rille based on the close associations of many venusian sinuous rilles with coronae we hypothesize that mantle plume or blob volcanism has caused high effusion and sustained lava eruptions essential for sinuous rille formation mantle derived high temperature low viscosity lava eruptions are responsible for the efficient erosional processes particularly for thermal erosion that seems to be at least partially required for some sinuous rille formation many valley networks are observed in highlands and in association with coronae fracture systems and source zones for low viscosity lavas both key to network formation were probably concentrated at highlands and coronae canali type channels which are morphologically unlike other known volcanic channels are limited to certain plains regions a wide range of low viscosity lava types is possible for the channel forming lava depending on the formation mechanism their lengths exceed the lengths of other common volcanic channel types on venus implying a large volume of lava and long duration of the eruption the close association of canali with plains regions implies that canali formation is probably related to the emplacement of plains a hypothesized global resurfacing event late in venusian history may be responsible for canali formation

lithospheric structure and tectonics at isidis planitia mars abstract we characterize the lithospheric structure of isidis planitia on mars by analyzing mars global surveyor and mars odyssey gravity and topography data using a flexural model of a thin elastic shell including bending and membrane stresses isidis planitia is a circular relatively flat plain formed near the end of the early noachian at the edge of the highlands lowlands boundary and the site of a large free air gravity anomaly features consistent with modification and filling of an impact basin our results suggest that the bulk density of the fill material inside isidis must be more than 2600 kg m 3 and higher densities are probable a comparison of the faulting observed at nili fossae to the predicted zone of extensional strain northwest of isidis constrains the thickness of the elastic lithosphere to be 100 180 km thick beneath the basin at the time of loading we also find that loads outside of the basin play a significant role in the interpretation of the tectonics simplified models tend to overestimate the lithospheric thickness we place relatively narrow bounds on the thermal gradient 3 4 6 5 k km 1 and heat flux 13 6 26 mw m 2 at isidis at the time of loading

elves triggered by positive and negative lightning discharges optical flashes in the lower ionosphere due to the transient heating caused by lightning electromagnetic pulses emp are unambiguously identified with the fly s eye photometric array data from a thunderstorm over mexico recorded at langmuir laboratory on august 27 1997 demonstrate that relatively common negative cloud to ground lightning is a previously unrecognized major cause of elves the spatial extent of the transient heating is shown optically to be typically at least 200 700 km laterally indicating the possibility for accumulation of ionization effects produced by successive flashes within large nighttime thunderstorm systems one especially bright event suggests that temporal fine structure in the causative very low frequency emp can manifest itself in the photometric record of elves

wrinkle ridge assemblages on the terrestrial planets the wrinkle ridge assemblage is a group of associated features that have been observed on the moon mars and mercury members of the wrinkle ridge assemblage are classified as either arches or ridges based on morphology and ridges are subdivided into first second or third order ridges on the basis of dimensions the ridge assemblages described in this study are known to occur in mare basalts on the moon and smooth plains units that may be volcanic in origin on mars and mercury the structures that occur in the continental flood basalts of the columbia plateau in the northwestern united states are morphologically and dimensionally similar to features in the ridge assemblages on the terrestrial planets the anticlinal ridges of the columbia plateau and many first order ridges on the moon mars and mercury are interpreted to be folds with reverse or thrust faulting developed as a result of buckling flexure fracture or buckling as a consequence of reverse or thrust faulting fracture flexure estimates of the unit shortening across first order ridges using simple geometric forms to approximate the ridge morphology are lower than those determined for the anticlines of the columbia plateau where displacements are the results of folding and reverse to thrust faulting evidence of layer parallel extension that often accompanies folds developed by fracture flexure mechanisms i e drape or fault bend folds is not found in the anticlinal ridges of the columbia plateau and has only been observed in one ridge on the moon a kinematic model involving buckling followed by reverse to thrust faulting flexure fracture is favored for the origin of the anticlinal ridges of the columbia plateau and many of the first order ridges on the moon mars and mercury

morphologic stratigraphic and morphometric investigations of valley networks in eastern libya montes mars implications for the noachian hesperian climate change dendritic valley networks and broad longitudinal valleys are widespread within the eastern libya montes region the morphologic characteristics of the studied dendritic valleys especially their occurrence at local summits provide evidence for the initial formation by surface runoff due to atmospheric precipitation whereas the longitudinal valley systems are thought to have been formed and modified by groundwater induced processes our crater counts and model ages show that the dendritic valley networks average age 4 0 ga formed earlier than the longitudinal valley systems average age 3 7 ga both fluvial forms indicate a temporal change of the erosive environment at the noachian hesperian transition at 3 8 ga our results suggest that the fluvial activity within our investigation area lasted for 800 my from 4 1 ga to 3 3 ga the dendritic valleys show valley densities between 0 12 km 1 and 0 57 km 1 indicative of highly mature and integrated valley systems that we interpret to be characteristic of warmer and wetter conditions on mars

fluid lava flows in gusev crater mars 1 rocks on the floor of gusev crater are basaltic in composition as determined from measurements by the mars exploration rover spirit on the basis of compositional data models of the basaltic lavas at the time of their emplacement suggest viscosities of 2 3 to 50 pa s dependent on the number of phenocrysts and vesicles that were present which would be more fluid than terrestrial tholeiitic lavas and comparable to mare lavas on the moon or archean high mg basalts on earth morphological data and crater counts derived from the high resolution stereo camera on mars express and other orbiters suggest that the lavas flooded gusev crater at about 3 65 b y and postdate older floor materials such as putative sediments emplaced by ma adim vallis

formation of venusian canali considerations of lava types and their thermal behaviors because liquid water is unstable at present venusian surface conditions the discovery of channels termed canali on venus thousands of kilometers long was not predicted low viscosity lavas that remain fluid for several thousand kilometers are considered to be the canali forming agents possible compositions of venusian canali forming lavas include komatiite and high fe ti lunar type basalts results of analytical and numerical models of these lavas reveal that total cooling is more efficient on venus than on earth suggesting that venusian lavas rapidly form insulating crusts and thus that the canali lavas were essentially tube fed the models also reveal that thermal erosion should be less efficient on venus than on earth suggesting that venusian channels are either the product of mechanical rather than thermal erosion or constructional processes

thermal erosion by laminar lava flows thermal erosion by hot lavas during their laminar flow over cold ground is investigated both theoretically and experimentally an analysis of the steady forced convective heat transfer by a laminar channel flow at large peclet numbers is presented which is used to determine the final steady state erosion velocity as well as the thicknesses and timescales of the associated thermal boundary layers in both the lava and ground the initial transient period involving the growth and remelting of a basal chill layer is also quantified laboratory experiments are described in which hot molten wax flowed over and thermally eroded an underlying bed of solidified wax the experimental observations of chill formation and thermal erosion are found to be in excellent agreement with the theoretical predictions the theory is applied to predict rates of thermal erosion consistent with those observed in recent flows of basaltic lava in hawaii and of carbonatite lava in tanzania

dynamic river channels suggest a long lived noachian crater lake on mars 1 recent images of the noachian age holden northeast crater show spectacular meandering channels that form a complex 150 meter thick lacustrine river delta deposit confined to the northwest margin of the crater we identify 11 major avulsion events in the topmost layer and suggest an avulsion frequency of a few hundred years the meandering nature of the channels and numerous avulsions is incompatible with deposition on an alluvial fan and clearly reflects a complex history of multiple sustained flows assuming an average sedimentation rate of 1mm year we suggest that holden ne crater contained a lake that persisted for at least 150 000 years our analysis is incompatible with this feature being the result of a major bolide impact that would have released a catastrophic flood by groundwater sapping and supports the hypothesis that early mars was both warmer and wetter during the noachian

compositional heterogeneity of the ancient martian crust analysis of ares vallis bedrock with themis and tes data 1 themis multispectral and thermophysical information combined with tes hyperspectral and albedo data is used as a powerful high spectral spatial resolution tool to investigate the mineralogic heterogeneity of ancient martian crust exposed in ares vallis bedrock three major spectral units are present in the upper ares vallis region 1 a regional unit that is composed primarily of a high silica si o 0 35 component with lesser amounts of plagioclase and pyroxene and is associated with channel wall rock and surrounding plains 2 a pyroxene and olivine rich rock unit exposed as a 250 m thick contiguous layer in the wall rock of ares vallis as well as in isolated exposures in the plains outside of the channel and 3 a unit composed of plagioclase pyroxene and lesser high silica component s si o 0 35 that primarily occurs as low albedo sand the spatial and stratigraphic distribution of these units suggests that the pyroxene and olivine enriched unit may be extrusive and or intrusive in origin indicating that this region experienced either a single stage or repeated episodes of olivine enriched magmatism during the first 1 5 gyr of crust formation this olivine enrichment may have been caused by a larger degree of mantle partial melting facilitated by higher mantle temperature melting from a more depleted mantle source and or less olivine fractionation relative to regional rock parent magmas the olivine rich unit is similar in thermophysical character to previously published olivine bearing terrains on mars but the derived modal mineralogy consists of 20 more pyroxene and less plagioclase than those terrains

forward mechanical modeling of the amenthes rupes thrust fault on mars amenthes rupes overlies one of the largest thrust faults on mars with structural topography accurately measured by mola forward mechanical models successfully predict the surface topography across this large contractional structure the best fitting fault parameters are fault dip angle 25 30 depth of faulting 25 30 km and fault offset 1 5 km these first order results are insensitive to either the offset distribution along the fault or crustal material properties both very shallow e g 15 km and very deep 45 km depths of faulting can be ruled out as can significantly different dips and offset magnitudes amenthes rupes may span the ancient seismogenic lithosphere in the martian noachian highlands implying maximum values at the time of faulting for heat flux of 54 70 mw m 2 and paleogeothermal gradient of 15 20 k km 1

groundwater controlled valley networks and the decline of surface runoff on early mars 1 fluvial erosion on early mars was dominated by valley networks created through a combination of groundwater processes and surface runoff a reduced greenhouse effect due to co 2 loss together with a declining geothermal heat flux promoted the growth of a cryosphere and a hesperian hydrologic regime dominated by outflow channel formation we test the hypothesis that the transition from valley network to outflow channel formation was preceded by a more subtle evolution characterized by a weakening of surface runoff leaving groundwater processes as the dominant final source of valley network erosion our hypothesis supported by a terrestrial analog in the atacama desert of chile is related to the groundwater sapping reactivation hypothesis for densely dissecting highland valley networks on mars suggested by baker and partridge in 1986 and focuses on the age analysis of large sparsely dissecting valley networks such as nanedi valles nirgal vallis valleys in fretted terrain and tributaries of outflow channels and valles marineris chasmata we find that these features are consistently late noachian to hesperian in age younger than noachian densely dissecting dendritic valley networks in the southern highlands in the tharsis region the observation of dense and sparse valley network morphologies on hesperian terrain suggests that while surface runoff gave way to groundwater processes consistent with our hypothesis the transition may have occurred later than elsewhere on the planet the volcanic nature of tharsis suggests that geothermal heat and volatile production led to episodically higher volumes of surface runoff in this region during the hesperian

catastrophic erosion of hellas basin rim on mars induced by magmatic intrusion into volatile rich rocks 1 malea and hesperia plana form large sectors of the rim of hellas basin that display partly eroded volcanic shields and plains these regions have topographic profiles that appear to be several hundred meters lower than those of adjacent rim sectors and lack prominent massifs of remnant basement that would be expected to stand above the lava plains we interpret that before the volcanic edifices were constructed these regions were denuded by an early stage of voluminous sill intrusion into friable volatile rich impact breccia magma volatile interactions may have resulted in catastrophic generation of debris flows deposited into the adjacent basin particularly if co2 were involved later lavas covered the eroded terrain in turn the lavas were eroded locally by volatile interactions across mars huge channel systems erosional features in volcanic terranes and vast layered deposits may be due to magma volatile interactions

geology of xanthe terra outflow channels and the mars pathfinder landing site the mars pathfinder landing site mpls was selected for its location at the mouths of ares and tiu valles outflow channels on mars where sediments from a variety of geologic units could have accumulated in a lacustrine environment recent geologic mapping at 1 2 m scale of the xanthe terra channels and chryse planitia near mpls reveals a progression of fluvial erosion and deposition throughout the hesperian period from the geology the watersheds of the channels were inferred and a sequence of paleogeologic maps was produced three outflow episodes are recognized 1 broad sheetwash during the early hesperian emanating from eastern valles marineris and equatorial chaos regions with initial erosion into highland plateau basement 2 early channel formation and 3 subsequent flooding which deepened the channels to their current morphologies the most recent flooding issued from simud and tiu valles during the late hesperian indicated by stratigraphic superposition striations along the floor of the channel and the orientation of streamlined islands in the flood direction this suggests that surface sediments deposited at mpls are most likely to have come from these channels and to a lesser extent from ares vallis a ranking scheme was developed to assess the potential origins for the sediments found at mpls the most abundant materials are inferred to have come from the noachian and hesperian highland plains and reworked sediments from previous floods underlying materials from earlier floods could also be found at mpls as ejecta from nearby impact craters

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

wrinkle ridges stress domains and kinematics of venusian plains wrinkle ridges are nearly ubiquitous landforms on the plains of venus by analogy with similar structures on other planets venusian wrinkle ridges are inferred to trend normal to the direction of maximum principal compression in the crust an inference that is verified by geometrical relationships with positive and negative relief features on venus because plains are the dominant terrain on venus wrinkle ridges provide an excellent opportunity to determine the orientations of shallow crustal principal stress trajectories over most of the planet in most places there are two or more sets of wrinkle ridges and commonly one of these persists over a very large area defining a regional stress domain intersection relationships indicate that these domains differ in age

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

more evidence for a one to one correlation between sprites and early vlf perturbations 1 past studies have shown a correlation between sprites and early vlf perturbations but the reported correlation varies widely from 50 to 100 the present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband vlf observations in which multiple transmitter receiver vlf pairs with great circle paths gcps passing near a sprite producing thunderstorm were available in this setup the multiple paths act in a complementary way that makes the detection of early vlf perturbations much more probable compared to a single vlf path that can miss several of them a fact that was overlooked in past studies the evidence shows that visible sprite occurrences are accompanied by early vlf perturbations in a one to one correspondence this implies that the sprite generation mechanism may cause also sub ionospheric conductivity disturbances that produce early vlf events however the one to one visible sprite to early vlf event correspondence if viewed conversely appears not to be always reciprocal this is because the number of early events detected in some case studies was considerably larger than the number of visible sprites since the great majority of the early events not accompanied by visible sprites appeared to be caused by positive cloud to ground cg lightning discharges it is possible that sprites or sprite halos were concurrently present in these events as well but were missed by the sprite watch camera detection system in order for this option to be resolved we need more studies using highly sensitive optical systems capable of detecting weaker sprites sprite halos and elves

global distribution composition and abundance of olivine on the surface of mars from thermal infrared data 1 we used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of fo91 fo68 fo53 fo39 fo18 and fo1 olivine samples to mars global surveyor thermal emission spectrometer tes data over low albedo regions of mars the fo91 fo68 fo53 and fo39 spectral end members were confidently identified on mars a range of compositions wider than inferred from martian meteorites small less than hundreds of square kilometers occurrences of the fo91 spectral end member are present in the rims of the argyre and hellas impact basins and may represent martian mantle materials the fo68 spectral end member is common throughout the highlands chasmata outflow channels and nili fossae region the fo53 spectral end member occurs in eastern syrtis major the nili fossae region and smooth floored craters of the highlands although less abundant than fo68 and fo53 the distribution of the fo39 spectral end member suggests that some olivine on mars is more fe rich than olivine in martian meteorites global maps of olivine show that 1 materials containing 10 20 of olivine are common in the southern highlands of mars 2 olivine is most common near the topographic dichotomy boundary and 3 olivine becomes uncommon near the poles suggesting that it may be influenced by topography and or latitude climate olivine is found in early noachian to amazonian terrains some of which may be coeval with phyllosilicate and sulfate deposits detected by omega implying that any early noachian wet period of mars climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

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

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

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

topography of small martian valleys abstract small valleys are common in the ancient highlands of mars valley widths are typically a few kilometers and are independent of length for valleys longer than about 50 km topographic profiles across several representative small valleys produced using one dimensional photoclinometry have smoothly curved shapes and valley side slopes of 10 20 profiles of unusual valleys from maumee valles the flanks of alba patera and softened terrain also have slopes of 10 20 but the profiles of maumee valles are more v shaped than those of the typical small valleys while the profiles of the softened valley have proportionately longer upslope convexities depths from 15 to 800 m are measured for the small martian valleys and most valleys have depths between 20 and 250 m the mean depth to width ratio from 135 measurements of 45 different valleys is 0 08 standard deviation 0 04 when valley profiles with uneven rims are excluded the mean depth to width ratio is 0 07 standard deviation 0 03 applying the lower ratio to the widths of a larger sample of small valleys yields depths that are almost all between 40 and 300 m the majority of the small valleys we have studied are probably the result of groundwater sapping and in this context the measured valley depths imply that liquid water was often less than a few hundred meters below the surface in the vicinity of these valleys at the time early in martian history when the valleys formed

the western libya montes valley system on mars evidence for episodic and multi genetic erosion events during the martian history a valley network in the western libya montes region extending from 80 e to 83 4 e and 1 2 s to 3 9 n exhibits significant detail about water release processes and duration of erosional activities the valley system originates at the southeastern offshoot of syrtis major and drains down to isidis planitia over a distance of about 300 km midstream the valley network splits into a shorter eastern and a longer western part for most of its length the valley exhibits an interior channel which allows constraining discharges ranging from 15 000 m3 s to 430 000 m3 s and yielding sediment volumes up to 250 tons s based on stratigraphic relations the valley system evolved during a period of about 2 8 billion years with major wet episodes in the noachian 4 1 ga the hesperian 3 6 to 3 0 ga and the amazonian 2 8 to 1 4 ga while precipitation dominated the fluvial activity during the noachian era as indicated by dendritic drainage pattern the close correlation of lava deposits and valley source regions suggests that volcanic processes such as ground ice melting and or hydrothermal water release might have played a major role during the hesperian and amazonian fluvial activities in addition multiple volcanic events in the hesperian and amazonian ages show that syrtis major was active at least locally until 1 4 ga ago discharge estimates demonstrate a significant increase from precipitation induced to volcanic triggered water release fluvial erosion rates discharges sediment transport rates and the lack of any widespread chemical alteration products such as sulphates and phyllosilicates that are indicative for large long lasting standing bodies of water suggest relatively short valley formation times of only a few thousands of years compared with the total age of the valley system short episodic water release events separated by long dry and inactive periods of some hundreds of millions of years at least in the hesperian and amazonian seem to be more realistic rather than a continuous flow the youngest channel segment dates back to less than 1 4 ga this indicates the presence of surface runoff at that time which required atmospheric conditions that support water to be stable on the surface even late in martian history in summary the western libya montes valley system demonstrates episodic and multi genetic erosion events over most of the martian history with a clear change in the erosion style from precipitation to volcanic triggered water release during the early hesperian

perturbations to the lower ionosphere by tropical cyclone evan in the south pacific region very low frequency vlf electromagnetic signals from navigational transmitters propagate worldwide in the earth ionosphere waveguide formed by the earth and the electrically conducting lower ionosphere changes in the signal properties are signatures of variations in the conductivity of the reflecting boundary of the lower ionosphere which is located in the mesosphere and lower thermosphere and their analysis is therefore a way to study processes in these remote regions here we present a study on amplitude perturbations of local origin on the vlf transmitter signals npm nlk naa and jji observed during tropical cyclone tc evan 9 16 december 2012 when tc was in the proximity of the transmitter receiver links we observed a maximum amplitude perturbation of 5 7db on jji transmitter during 16 december event from long wave propagation capability model applied to three selected events we estimate a maximum decrease in the nighttime d region reference height h by 5 2 km 13 december npm and maximum increase in the daytime d region h by 6 1 km and 7 5 km 14 16 december jji the results suggest that the tc caused the neutral densities of the mesosphere and lower thermosphere to lift and sink bringing the lower ionosphere with it an effect that may be mediated by gravity waves generated by the tc the perturbations were observed before the storm was classified as a tc at a time when it was a tropical depression suggesting the broader conclusion that severe convective storms in general perturb the mesosphere and the stratosphere through which the perturbations propagate

characteristics of long recovery early vlf events observed by the north african awesome network 1 lightning strokes are capable of initiating disturbances in the lower ionosphere whose recoveries persist for many minutes these events are remotely sensed via monitoring subionospherically propagating very low frequency vlf transmitter signals which are perturbed as they pass through the region above the lightning stroke in this paper we describe the properties and characteristics of the early vlf signal perturbations which exhibit long recovery times using subionospheric vlf transmitter data from three identical receivers located at algiers algeria tunis tunisia and sebha libya the results indicate that the observation of long recovery events depends strongly on the modal structure of the signal electromagnetic field and the distance from the disturbed region and the receiver or transmitter locations comparison of simultaneously collected data at the three sites indicates that the role of the causative lightning stroke properties e g peak current and polarity or that of transient luminous events may be much less important the dominant parameter which determines the duration of the recovery time and amplitude appears to be the modal structure of the subionospheric vlf probe signal at the ionospheric disturbance where scattering occurs and the subsequent modal structure that propagates to the receiver location

hydrogeologic evolution of gale crater and its relevance to the exobiological exploration of mars abstract the presence of an amazonian impact crater lake in the noachian crater gale located in the aeolis northwest subquadrangle of mars is indicated by evidence from young floor deposits streamlined terraces layers and channels observed on the central sedimentary deposit evidence for the filling of this lake by two processes is described a the drainage of the aquifer in the aeolis mensae region supported by extended mass wasting and rim sliding in the crater at the contact with the mensae and b the overspilling of the northern rim by an amazonian south transgression of the elysium basin this last hypothesis is supported by hydrologic features such as channels and channel like depressions north of the crater and by the crescent like shape of the central sedimentary deposit the presence of an impact melt sheet and uplifted central peak may have also generated hydrothermal activity including an early crater lake shortly after the formation of the crater in the noachian period with time decreasing heat flux and changing climates gale may have experienced transitions in aqueous environments from warm and wet to cold and ice covered water that could have provided suitable oases for various communities of microorganisms preservation of the biological and climatic record may have been favored in this paleolacustrine environment which probably occured episodically over two billion years

duration of the ma adim vallis gusev crater hydrogeologic system mars abstract ma adim vallis and gusev crater aeolis subquadrangle of mars formed a complex hydrogeologic system through time crater statistics over five geologic units coupled with morphologic and geologic observations show that this system was active over a period ranging from 0 7 to about 2 billion years these results make the floor of gusev crater one of the most prominent martian depositional features the last aqueous sedimentary deposition could have occurred during early amazonian

an igneous origin for features of a candidate crater lake system in western memnonia mars the association of channels inner terraces and delta like features with martian impact craters has previously been interpreted as evidence in favor of the past existence of crater lakes on mars however examination of a candidate crater lake system in western memnonia suggests instead that its features may have formed through igneous processes involving the flow and ponding of lava accumulations of material in craters and other topographic lows throughout much of the study region have characteristics consistent with those of volcanic deposits and terraces found along the inner flanks of some of these craters are interpreted as having formed through drainage or subsidence of volcanic materials channels previously identified as inlets and outlets of the crater lake system are interpreted instead as volcanic rilles these results challenge previous interpretations of terrace and channel features in the study region and suggest that candidate crater lakes located elsewhere should be reexamined

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

mineralogy of the nili fossae region with omega mars express data 2 aqueous alteration of the crust 1 nili fossae is a region with fresh exposures of old material omega spectral data have revealed a strong diversity of minerals in the nili fossae region including mafic minerals and phyllosilicates phyllosilicates are found to be primarily fe rich smectites a type of clay minerals these phyllosilicates are observed only on the noachian crust in four types of locations three are without any signatures other than phyllosilicates on 1 smooth layered deposits 2 massive exhumed material and 3 crater ejecta and one type of location is associated with olivine 4 over an altered mafic unit this diversity suggests a widespread liquid water activity and a variety of alteration processes the formation of phyllosilicates underwent considerable reduction if not cessation by the time of formation of syrtis major lava flows in the hesperian period phyllosilicates are spatially and chronologically disconnected from the fluvial and depositional landforms observed in the nili fossae region observations suggest that these landforms formed after the extensive formation of phyllosilicates during short periods of time and or temperatures close to freezing

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

seismotectonics of the amenthes rupes thrust fault population mars 1 thrust faults within the amenthes rupes population in eastern mars accommodated contractional strains of 0 06 with total cumulative moment energy release of 2 1024 mj during late noachian time small faults that scale three dimensionally accommodate only 12 17 of the strain and 6 9 of the moment release indicating that inventories of martian faults need not be complete down to the smallest lengths for meaningful estimates of strain and moment to be obtained frictional stability relations for martian lithosphere suggest that most 83 of the largest fault amenthes rupes was seismogenic during displacement accumulation with smaller faults being progressively less seismogenic as shallower depths are penetrated with decreasing fault lengths given plausible displacement rates from terrestrial intraplate thrust faults of 1 0 01 mm yr 1 the amenthes fault population may have taken as little as 1 5 m y to grow into its present configuration corresponding to slow homogeneous strain rates of 10 17 s 1 or less that are comparable to those of terrestrial plate interiors

origin of periodically spaced wrinkle ridges on the tharsis plateau of mars ridged plains are a major geologic unit on mars and are a predominant unit on the tharsis plateau a region that has undergone uplift extension and extensive shield and flood volcanism these units probably flood volcanic in origin are characterized by landforms classed as wrinkle ridges wrinkle ridges are interpreted to be folds resulting from buckling followed by reverse to thrust faulting flexure fracture a prominent characteristic of many of the wrinkle ridges on mars particularly those in the tharsis ridge system is the periodic nature of their spacing the periodic spacing has been evaluated in six major provinces on the tharsis plateau with regions further divided into domains based largely on variation in ridge orientation the average spacing of the tharsis ridges based on 2934 measurements is 30 km in an effort to account for the periodic nature of the wrinkle ridges the ridged plains material is modeled as both a single member and a multilayer with frictionless contacts that has buckled at a critical wavelength of folding free slip between layers is assumed based on the possible existence of mechanically weak interbeds in the ridged plains sequence separating groups of flows the near surface mechanical structure in the area of ridged plains is approximated by a strong layer or layers overlying a weak megaregolith of finite thickness overlying a strong basement buckling of the ridged plains is assumed to be decoupled from the basement by the weak megaregolith decoupling is enhanced if the megaregolith were water or ice rich at the time of deformation the rheologic behavior of the ridged plains and megaregolith is approximated by a linear elastic and linear viscous material the models are examined for a range in 1 the strength contrast between the ridged plains material and the underlying megaregolith 2 thickness of the ridged plains material 3 thickness of the megaregolith and 4 number of layers the elastic model can explain the observed ridge spacing only if the ridged plains are relatively thick 2400 m with multiple layers n 1 and relatively high contrasts in young s modulus e e0 100 the high e e0 required is possible only if the megaregolith was water rich at the time of deformation over the same range in values of the parameters viscous buckling is much less restricted the viscous model can explain the observed ridge spacing over a wide range in ridged plains thickness 250 m to several kilometers megaregolith thickness number of layers n 1 to 8 and contrasts in viscosity 0 10 in addition viscous buckling is viable if the megaregolith were dry water rich or ice rich at the time of deformation the absence of folds with a cross sectional geometry in the shape of a sinusoid anticline syncline pairs may be the result of initial deformation of the ridged plains material into low amplitude folds in infinitesimal strain followed by plastic yielding in the cores of the anticlines in finite strain initial elastic or viscous buckling coupled with plastic yielding confined to the hinge area followed by the development of reverse to thrust faulting could account for the asymmetric fold geometry of many of the wrinkle ridges

geomorphology of ma adim vallis mars and associated paleolake basins 1 ma adim vallis one of the largest valleys in the martian highlands appears to have originated by catastrophic overflow of a large paleolake located south of the valley heads ma adim vallis debouched to gusev crater 900 km to the north the landing site for the spirit mars exploration rover support for the paleolake overflow hypothesis comes from the following characteristics 1 with a channel width of 3 km at its head ma adim vallis originates at two eastern and western gaps incised into the divide of the 1 1 m km2 enclosed eridania head basin which suggests a lake as the water source 2 the sinuous course of ma adim vallis is consistent with overland flow controlled by preexisting surface topography and structural control is not evident or required to explain the valley course 3 the nearly constant 5 km width of the inner channel through crater rim breaches the anastomosing course of the wide western tributary the migration of the inner channel to the outer margins of bends in the valley s lower reach a medial sedimentary bar 200 m in height and a step pool sequence are consistent with modeled flows of 1 5 106 m3 s peak discharges were likely higher but are poorly constrained by the relict channel geometry 4 small direct tributary valleys to ma adim vallis have convex up longitudinal profiles suggesting a hanging relationship to a valley that was incised quickly relative to the timescales of tributary development 5 the eridania basin had adequate volume between the initial divide and the incised gap elevations to carve ma adim vallis during a single flood 6 the eridania basin is composed of many overlapping highly degraded and deeply buried impact craters the floor materials of the six largest craters have an unusually high internal relief 1 km and slope 0 5 1 5 among degraded martian craters which are usually flat floored long term fluvial sediment transport appears to have been inhibited within these craters and the topography is inconsistent with basaltic infilling 7 fluvial valleys do not dissect the slopes of these deeper crater floor depressions unlike similar slopes that are dissected at higher levels in the watershed these characteristics 6 7 suggest that water mantled at least the lower parts of the eridania basin floor throughout the period of relatively intense erosion early in martian history the lake level increased and an overflow occurred near the close of the noachian age determined using 5 km crater counts initially the eridania basin debouched northward at two locations into the intermediate basin a highly degraded impact crater 500 km in diameter as this intermediate basin was temporarily filled with water erosion took place first along the lower northern reach of ma adim vallis debouching to gusev crater the western overflow point was later abandoned and erosion of the intermediate basin interior was concentrated along the eastern pathway subsequent air fall deposition impact gardening tectonism and limited fluvial erosion modified the eridania basin region so evidence for a paleolake is restricted to larger landforms that could survive post noachian degradation processes

hydrovolcanic tuff rings and cones as indicators for phreatomagmatic explosive eruptions on mars hydrovolcanism is a common natural phenomenon on earth and should be common on mars too since its surface shows widespread evidence for volcanism and near surface water we investigate fields of pitted cones in the nephentes amenthes region at the southernmargin of the ancient impact basin utopia which were previously interpreted as mud volcanoes the cone fields contain pitted and breached cones with associated outgoing flow like landforms based on stratigraphic relations we determined ahesperian or youngermodel age we test the hypothesis of a hydro volcanic origin based on a detailed morphological and morphometrical analysis and an analysis of the regional context an igneous volcanic origin of these cones as hydrovolcanic edifices produced by phreatomagmatic eruptions is plausible several lines of evidence suggest the existence of subsurface water ice the pitted cones display well developed wide central craters with floor elevations below the preeruptive surface their morphometry and the overall appearance are analogous to terrestrial tuff cones and tuff rings mounds that are also observed in the same region resemble terrestrial lava domes the hydrovolcanic interaction between ascending magma and subsurface water and or water ice may explain the formation of the pitted cones although other scenarios such as mud volcanism cannot be ruled out together with the mounds the cones might represent effusive and explosive edifices of amonogenetic volcanic field composed of lava domes tuff rings tuff cones and possibly maars

a description of surface features in north tyrrhena terra mars evidence for extension and lava flooding abstract we studied north tyrrhena terra an approximately 39 000 km 2 area located in the transition region straddling the amenthes and mare tyrrhenum mars chart quadrangles 14 and 22 respectively the study area comprises ancient terrains with infilled craters ridges and valleys interpretation of orbiter data of ancient terrains is inherently difficult but valuable information can be obtained using multiple datasets and analyzing various geological features using data from the high resolution stereo camera on board mars express complemented by mars global surveyor mola dem and moc narrow angle datasets we observed and interpreted surface morphologies at a scale suitable for geologic investigation morphometric examination of a 31 km diameter large impact crater indicated that tectonism and volcanism were responsible for its morphologic modification small impact crater depth diameter relationships indicated that smooth surfaces of valleys are composed of highly consolidated material surface cracks and lobate fronts further suggested that the rocks are volcanic examination of tectonic features revealed that in the study area a dominant nw se fabric is related to a ridge bench scarp valley repetition consistent with synthetic and antithetic normal faulting a nnw sse lineament represents the surface expression of normal faulting post dating all other tectonic features a weak ne sw fabric is observable as small sublinear depressions and at the contact between units internal to one large crater one 20 km diameter crater in the study area was interpreted to be a caldera infilled by thick volcanic rock layers identification of wrinkle ridges further indicated that thick layered lava flows infilled the main depressions of the study area the available evidence suggests that the study area underwent multiple episodes of extension and volcanism

recent aqueous environments in martian impact craters an astrobiological perspective the discovery of gullies and debris aprons raises the question of the existence of aqueous environments on mars in recent geological times and its astrobiological implications three cases of such environments are surveyed at moc high resolution in the e gorgonum chaos and newton and hale craters the regional setting of these craters suggests that the mechanisms of aquifer destabilization flow discharge and gully formation in these three cases result from local geological triggers that can include impact cratering and tectonic processes rather than climate or insolation factor we take as a working hypothesis that microbial life appeared on mars in ancient geological times probably in a geothermal environment but potentially evolving via infrared detection systems to give photosynthetic communities under the selective pressure of energetic solar radiation we hypothesize that some microbial communities could have survived underground in either dormant or active state or that their biomolecules could be preserved either frozen or desiccated in the subsurface beneath the upper oxidized zone we assess the known environmental constraints for life and what type of potential habitats are provided in these three craters by aquifer discharges using comparison with terrestrial analogues and their associated microbial communities these environments include 1 the release of water on a dry crater floor in e gorgonum and the possibility for microorganisms and preserved biomolecules to be flushed out and mixed in with the sediment exposed at the surface 2 the evidence of a recent lacustrine episode in the newton crater with analogy to antarctic dry valley lakes 3 the exposure on the floor of hale crater of material from a regional subsurface that is likely to have retained traces of one of the oldest martian bodies of water recognized to date parker et al 2000 in the argyre basin we show how the water in argyre 3 8 billion years ago gya was likely to have been alterated by hydrothermal processes and how the subsequent formation of the 150 km hale crater on the northern ring of argyre generated hydrothermal pumping this accounts for the anomalously high location of the springs on the crater crests today with respect to the rest of the regional subsurface distribution finally we envision current impact cratering as a factor for destabilizing aquifers on mars today thus creating new environments we analyze the implications of impacts for two geological types of rock units that could harbor traces of life as a result we compare the potential of astrobiological exploration of crater floors rims and ejecta on future missions to mars

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

subionospheric early vlf signal perturbations observed in one to one association with sprites 1 observations on the night of 21 july 2003 of the ionospheric effects of a thunderstorm in central france are reported from 0200 to 0315 ut a camera system in the pyrenees mountains captured 28 sprites triggered by cg lightning as observed by the french meteorage lightning detection system a narrowband vlf receiver located on crete at 2200 km southeast of the storm observed subionospheric vlf signals from six ground based transmitters the amplitude of one of the vlf signals originating at a transmitter located 150 km west of the storm and passing through the storm region exhibited rapid onset perturbations occurring in a nearly one to one relationship with the optical sprites these early vlf events are consistent with a process of narrow angle forward scattering from a volume of enhanced ionization above the storm with lateral sizes larger than the vlf radio wavelength the many cg and cg discharges that did not produce sprites were also found to not be associated with detectable vlf amplitude perturbations even though some of these discharges reached relatively large peak currents the rapid onsets of several of the sprite related vlf perturbations were followed by relatively long onset durations ranging from 0 5 to 2 5 s indicating that these events were early but not fast these early slow events may suggest a slow process of ionization build up in the lower ionosphere following intense lightning discharges that also lead to sprites a limited number of early vlf perturbation events were also associated with whistler induced electron precipitation events or classic trimpi perturbations undoubtedly produced by the precipitation of electrons due to whistler mode waves injected into the magnetosphere by the same lightning flash that led to the production of the sprite

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

late cenozoic reverse faulting in the fall zone southeastern virginia abstract a set of en echelon reverse faults cut paleozoic metamorphosed igneous rocks of the piedmont and overlying late cenozoic sediments at the old hickory heavy mineral deposit in the fall zone of southeastern virginia diorite of the eastern slate belt was faulted over nearshore to shore face deposits of the pliocene yorktown formation these nw se striking faults experienced oblique dip slip movement with a maximum displacement of up to 6 m on individual faults faults tip out along strike and are overlain by distinct cobble beds suggesting that sediment deposition and faulting were contemporaneous deformation at old hickory may have been formed by reactivation of existing paleozoic structures under a regionally extensive compressional stress field parallel to the modern one

meander properties of venusian channels venusian channels which probably are lava channels have meander properties that relate to their mode of formation their channel meanders probably formed in response to flow dynamics as in the case of terrestrial rivers but low sinuosity indicates less developed morphology the meanders generally follow terrestrial river trends for wavelength l to width w ratios suggesting an equilibrium adjustment of channel form slightly higher l w in comparison to terrestrial rivers occurs for venusian channel types other than sinuous rilles the unusually low l w values for some venusian and lunar sinuous rifles probably indicate modification of original meander patterns by erosional channel widening by lavas the slightly larger radius of curvature to wavelength ratios of venusian channels may be attributed to the short time during which the lava channels formed and or they may represent a quasi equilibrium state for the system multiple wavelength meanders of specific venusian channels may have resulted from changes in discharge or from structural control

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

on the relationship between lightning peak current and early vlf perturbations 1 lightning strokes are known to cause direct heating and ionization of the d region some of which are detected via scattering of vlf transmitter signals and are known as early vlf events the disturbed ionosphere typically recovers in many tens of seconds new experimental evidence is presented demonstrating that the scattering pattern and onset amplitude of early vlf events are strongly related to both the magnitude and polarity of causative lightning peak current observations of early vlf events at nine stanford vlf receiver sites across the continental united states are combined with lightning geolocation data from the national lightning detection network nldn during january and march 2011 nldn recorded 7769 intense lightning discharges with high peak currents 100 ka generating 1250 detected early vlf events we show that the size of the scattered field due to the ionospheric disturbance increases with the peak current intensity of the causative lightning discharge the most intense peak currents of 200 and 250 ka disturb vlf transmitter signals as far as 400 km away from the lightning stroke early vlf event detection probability also increases rapidly with peak current intensity on the other hand the observed vlf amplitude change is not significantly dependent on the peak current intensity stroke polarity is also important with positive strokes being 5 times more likely to generate early vlf disturbances than negative strokes of the same intensity intense positive cloud to ground lightning discharges especially when occurring over the sea are also more likely to produce early vlf events with long recovery many minutes

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

geomorphological evidence of water level changes in nepenthes mensae mars in the western sector of nepenthes mensae mars there are some geomorphological features that could be related to a standing water sheet in the area such as fluvial terraces deltas and shorelines a detailed analysis of these features reveals two variations in water level probably related to tectonic processes as suggested by the existence of a fissural volcano at this site

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

recovery signatures and occurrence properties of lightning associated subionospheric vlf perturbations subionospheric vlf signatures of lightning associated ionospheric disturbances observed at multiple sites in the central united states are used to investigate the occurrence properties and recovery signatures of characteristic perturbations exhibiting rapid onset followed by slow recoveries the two different types of events so called early fast and lightning induced electron precipitation lep inan et al 1996a are distinguished by the lack of presence of a few hundred millisecond delay between vlf event onsets and causative lightning discharges respectively analysis of recovery signatures of the two types of events indicate subtle but distinct differences in the recovery rates a majority of early fast events were found to exhibit a more rapid initial recovery to preevent levels during the first 20 s of recovery when compared to lep events this experimental evidence indicates that the physical nature of the ionospheric disturbance involved in the two classes of events are different consistent with a recent theoretical suggestion inan et al 1996c the occurrence properties of early fast events observed by the holographic array for ionospheric lighting hail receivers indicate that ionospheric disturbances act primarily as forward scatterers

the evolution of lacustrine environments on mars is mars only hydrologically dormant abstract this study surveys the evolution of martian impact crater paleolakes through time by establishing their age comparing their locations and describing the formation of lacustrine sedimentary structures and features over time we explore their meaning in terms of global climate changes but also on local and regional scales we observe a co location between recent impact crater paleolakes and regions where gcm modeling shows that mars is currently experiencing days above triple point and below boiling point of water some source areas show morphologies that could be consistent with ancient glacier features in the argyre basin darwin crater region in locations that are also consistent with gcm models of past snow precipitation on mars we propose that at least for some paleolakes our results are best explained by recent and abundant aqueous activity on mars with some meteorological contribution these results are supported by other recent findings on martian meteorite ages by the analysis of new mgs data showing recent volcanic and fluvial activity and by climate modeling they point toward the possibility that mars currently is only hydrologically dormant and that there is a potential for hydrological activity to be generated again in the future following changes in the planet s orbital parameters

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

vlf observations of ionospheric disturbances in association with tles from the eurosprite 2007 campaign 1 two very low frequency vlf awesome remote sensing systems located at algiers algeria 36 45 n 3 28 e and sebha libya 27 02 n 14 26 e monitor vlf signal perturbations for evidence of ionospheric disturbances during the eurosprite 2007 campaign a number of transient luminous events tles were captured over the mediterranean sea by cameras at pic du midi 42 94 n 0 14 e and at centre de recherches atmospheriques cra in southwestern france 43 13 n 0 37 e the cameras observations are compared to collected vlf awesome data we consider early vlf perturbations observed on 12 13 17 18 october and 17 18 december 2007 the data from the two vlf receivers confirm the association between tles and early vlf signal perturbations with the perturbations amplitudes dependent on the observation configuration i e whether the tle is near the receiver near the transmitter or far from both and the scattering process the results also reveal that the early vlf perturbations can occur in the absence of a tle

ma adim vallis revisited through new topographic data evidence for an ancient intravalley lake abstract based on a comprehensive study of the recent topographic map usgs mc 23 se i 2119 usgs 1991 topographical map of aeolis plus geomorphic and digital elevation we have constructed a geometric model of ma adim vallis the sedimentary history of the valley was determined by the damming of the valley by two impact craters one by the southern crater over gusev rim and the second located 120 km upstream the presence of an intravalley lake system is inferred from independent sedimentary analysis and from geomorphic evidence for valley benches peripheral and parallel topographic contour intervals of the putative intravalley lake shores suggest that the lake was covered by a thick ice sheet the longitudinal profile of the valley floor shows a peculiar reverse slope located 300 km upstream from the southern gusev crater rim we conclude that this is an accumulation of sedimentary deposits adjacent to the crater rampart which defined the northern boundary of the lake when the water level reached the lowest point of the west bank which is 0 4 km below the top of the rim of gusev crater it began to floor the surrounding plateau as the intravalley lake level raised its ice cover formed a wide lateral bench later this ponded water was funneled into gusev crater through the breaching of the southern gusev rampart by an impact crater the paleolacustrine sediments transported by the lake water that channeled through the rampart debris slope mantled the floor of gusev crater the sublacustrine sediments are promising targets for future missions and of high priority in the search for past life

heavy mineral deposits in the upper coastal plain of north carolina and virginia approximately 22 7 million metric tons 25 million short tons of heavy minerals at an average grade of 6 wt percent in 377 8 million metric tons 416 million short tons of sand have been delineated in 19 deposits in the upper coastal plain of north carolina and virginia average concentrations of the principal minerals are ilmenite 60 percent rutile 2 5 percent zircon 12 5 percent staurolite 8 5 percent tourmaline 0 7 percent kyanite 3 0 percent sillimanite 1 3 percent and others principally limonite 11 5 percent these deposits formed during a worldwide pliocene transgressive regressive event that occurred between 3 5 and 3 0 ma the deposits formed as beach or dune sands during the regressive phase of the event over an elevation range of 96 m 315 ft to 53 m 175 ft other major deposits that are interpreted to have formed during the pliocene transgressive regressive event are as follows trail ridge florida enneaba western australia lakehurst new jersey and deposits of the western murray basin victoria australia combined reserves of these pliocene deposits exceed 317 5 million metric tons 350 million short tons of heavy minerals the potential for new discovery of pliocene deposits elsewhere in the world is judged to be favorable

multi instrumental observations of a positive gigantic jet produced by a winter thunderstorm in europe 1 at 2336 56 utc on 12 december 2009 a bright gigantic jet gj was recorded by an observer in italy forty nine additional sprites elves halos and two cases of upward lightning were observed that night the location of the gj corresponded to a distinct cloud top 34 c west of ajaccio corsica the gj reached approximately 91 km altitude with a trailing jet reaching 49 59 km matching with earlier reported gjs the duration was short at 120 160 ms this is the first documented gj which emerged from a maritime winter thunderstorm only 6 5 km tall showing high cloud tops are not required for initiation of gjs in the presence of strong vertical wind shear the meteorological situation was different from typical outbreaks of fall and winter thunderstorms in the mediterranean during the trailing jet phase of the gj a sprite with halo triggered by a nearby cloud to ground lightning flash occurred at a relatively low altitude 72 km at the same time the trailing jet and beads were reilluminated electromagnetic waveforms from hungary poland and the usa revealed this gj is the first reported to transfer negative charge approximately 136 c from the ionosphere to the positively charged origins in the cloud i e a positive cloud to ionosphere discharge ci with a large total charge moment change of 11600 c km and a maximum current of 3 3 ka early vlf transmitter amplitude perturbations detected concurrently with the gj confirm the production of large conductivity changes due to electron density enhancements in the d region of the ionosphere

admittance estimates of mean crustal thickness and density at the martian hemispheric dichotomy 1 admittance estimates from line of sight los acceleration profiles of the mars global surveyor spacecraft are used to constrain the mean crustal thickness and surface density centered on the hemispheric dichotomy from 110 e to 220 e 40 s to 20 n models with uniform crustal properties predict lower than expected bulk crustal densities two layer models with loading only at the surface and the moho produce satisfactory fits to the data the best fit surface density crustal thickness tc and elastic thickness te are 2 5 mg m 3 27 km and 61 km respectively higher elastic thicknesses require lower crustal thicknesses and vice versa the best fit ratio of moho to surface loading f is close to 1 models with no bottom loading f 0 provide a poor fit to the data underestimates in f result in underestimates of both tc and te the surface density is lower than that measured from martian meteorites and by admittance analyses of young volcanoes but is well constrained by the short wavelength admittance values for misfits up to 1 5 times the minimum value and a fixed surface density of 2 5 mg m 3 the ranges of tc te and f are 1 75 km 37 89 km and 0 4 2 6 respectively the apparently compensated nature of the large impact basins has been used to infer a lower bound on southern hemisphere crustal thickness of 45 km if this estimate is correct the likely mean crustal thickness in the area considered is 55 20 km

ancient martian volcanoes in the aeolis region new evidence from mola data mars orbiter laser altimeter mola altimetric data confirm the volcanic origin of a noachian aged hilly feature zephyria tholus in the aeolis area of mars similar characteristics shared by at least one nearby topographic high suggest that volcanic activity represented by such features may have been more widespread than previously thought morphological structures and morphometric data for zephyria are consistent with a stratovolcano origin in which the edifice formed by mixed explosive and effusive eruptions and was altered by subsequent flank erosion to produce a distinctive truncated cone with concave upward flanks criteria are outlined to help detect and distinguish the origin of such features in other ancient regions of mars

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

sequence and mechanisms of deformation around the hellas and isidis impact basins on mars the distribution and age of early volcanic and tectonic features surrounding the itellas and isidis impact basins are shown to fit a four stage sequence first concentric canyons form outside the basin boundary scarp at or near the time of basin formation followed shortly thereafter by radial troughs extending beyond the boundary scarp after a hiatus concentric graben develop inside the basin within the massif ring finally soon after graben formation widespread volcanic plains are emplaced between the massif ring and the boundary scarp to one side of the basin three models of basin centered deformation are compared io hese observed deformation events elastic flexure due to loading elastic flexure due to uplift and impact fracture a central load of basin fill can account for concentric fractures by elastic flexure around the load formation of the distant concentric canyons however requires lithospheric thicknesses a factor of 5 greater than those indicated by planetary thermal history models and an increase in feature width by an order of magnitude relative to flexural graben identified elsewhere on mars and the moon although inclusion of loading by basin ejecta reduces the required lithospheric thickness to acceptable values flexure still fails to account for the large canyon widths observed impact fracture from a rapid inward flow of asthenosphere during transient cavity collapse however is consistent with the three key observational constraints for the distant canyons their age width and distance from the basin as the basin then undergoes isostatic uplift soon after impact elastic flexure induces a radial pattern of failure consistent with the observed extent and timing of the radial troughs later after a long period of basin infilling elastic failure due to loading of the central basin region can account for the ring grabens in the massif ring the localization of volcanism into a single ridged plains unit on the basin rim indicates a thermal source offset from the basin which is not included in these models and perhaps reflects an additional mechanism unique to mars

palaeoflow reconstruction from fan delta morphology on mars abstract alluvial fans and deltas on mars record past hydrological conditions until now these conditions have been inferred from the morphology of the feeder channels and the deposits from images and digital terrain models dtms and from calculations of the bulk fluxes of water and sediment based on the dimensions of upstream channels neither method can distinguish between dilute river like flows and dense sediment laden flows however while the formation time scales for these two sediment transport modes differ by orders of magnitude the objective of this paper is to compare dtm data quantitatively with a morphological model to infer sediment transport mode and formative duration we present a quantitative morphological model for fan and delta formation that assumes as little as possible the model calculates the growth of a sedimentary body in a crater lake represented by a low gradient subaerial cone on top of a high gradient subaqueous cone the volume of the cone is constrained by the influx of sediment while the elevation of the break in slope that is the shoreline is constrained by the influx of water the water and sediment fluxes were calculated with physics based predictors based on the feeder channel small scale morphology such as crater wall irregularities concavity of the fan surface and channel avulsion is ignored the model produces alluvial fans stair stepped fan deltas and gilbert fan deltas as well as hitherto unidentified crater wall drapes the parameters that determine which morphology emerges are the supply of sediment and water to the basin the size of the basin and the duration of the flow a direct comparison between the cone model and hrsc dtm data for five deltas and an alluvial fan demonstrates that single event dilute flows of short duration days to years have created all of the deposits two gilbert fan deltas were formed in overspilling crater lakes from long low gradient upstream channels one alluvial fan was formed in a similar manner except that the damaged crater did not lead to ponding three stair stepped deltas were formed from short high gradient upstream channels that only partially filled the crater lakes

tyrrhena patera geologic history derived from mars express high resolution stereo camera 1 we used mars express high resolution stereo camera images of the tyrrhena patera volcano to assign cratering model ages to material units defined in the vikingorbiter based geologic mapping cratering model ages are generally consistent with their stratigraphy we can identify three key intervals of major activity at tyrrhena patera 1 formation of the volcanic edifice in the noachian period 3 7 4 0 ga shortly following the hellas impact 4 ga and coincident with the formation of hadriaca patera 3 9 ga 2 modification of the edifice and formation of the caldera rille and channels in the hesperian period possibly extending into the amazonian period and 3 a final stage of modification in the late amazonian epoch 0 8 1 4 ga early to mid hesperian activity on tyrrhena patera is consistent with similar activity on hadriaca patera at 3 3 3 7 ga the most recent dateable event on tyrrhena patera is modification on the upper shield caldera rille and channel floors at 800 ma this coincidence of resurfacing in three units suggests a widespread process es which we speculate involved preferential aeolian erosion of small craters on these flatter surfaces relative to the other units on the volcano alternatively some combination of pyroclastic flow emplacement on the upper shield and fluvial activity in the caldera rille and channels followed by differential aeolian erosion and deposition could have produced the present surface regardless major geologic resurfacing ended at tyrrhena patera nearly a billion years ago

volcanic processes as alternative mechanisms of landform development at a candidate crater lake site near tyrrhena patera mars 1 palos crater a prominent candidate crater lake site in the hesperia region of mars is located at the mouth of a sinuous inlet channel that extends from the northern flanks of tyrrhena patera previous studies of this site have concluded that channels and basin infill units likely formed through aqueous processes that partly involved karst like removal of materials in the subsurface by the flow of groundwater as with many locales on mars the aqueous processes hypothesized to have been involved in the formation and evolution of terrain features are compelling however the characteristics of this site suggest that an alternative set of mechanisms for landform development should be considered alongside aqueous hypotheses the main attributes of channels and infill of the central crater include 1 an association with a very large volcanic rise to the south 2 the existence of roofed segments of the main inlet channel and 3 infill of the central crater and outlet channel by materials that have characteristics consistent with those expected of volcanic plains these general attributes are consistent with formation through or in association with processes that involved the flow of lava although a volcanic model may account for the presence and basic nature of landforms previously considered supportive of a paleolake interpretation of the site an overprint of dendritic valley networks on parts of the inlet system suggests that aqueous processes may have also acted in the evolution of the site a complex interrelation between past igneous and aqueous processes at this site is possible

resurfacing of the martian highlands in the amenthes and tyrrhena region the southern cratered highlands of mars contain a large population of flat floored rimless craters which have previously been interpreted to have formed by aeolian mantling or flood volcanism neither of these geologic processes accurately explains the observed morphology or the crater statistics geologic mapping in the amenthes and tyrrhena region indicates that craters with this morphology occur on undulating intercrater materials near the dichotomy boundary and on more rugged materials farther into the highlands containing numerous ancient valley networks cumulative size frequency distribution curves indicate ages of n 5 790 early to middle noachian and n 5 540 middle noachian for the cratered plateau and cratered highland materials respectively opposite the observed stratigraphic relations for crater diameters 16 km the population of impact craters is consistent with stratigraphy but the population of smaller craters in the region indicates the importance of resultacing superposed fresh craters indicate a resultacing event that ceased at n 5 200 250 late noachian to early hesperian crater counts divided into 5 o latitudinal bins show an increase in the number of craters between the 8 and 50 km diameter range with increasing northerly latitudes suggesting that the resurfacing was not a single event statistical modelling of an erosive event capable of removing the continuous ejecta deposits from the craters eroding them to reduce the apparent diameter and simultaneously burying smaller eroded craters explains both the morphology of the flat floored rimless craters and their population distribution matching the slope of the modelled curves with that of the cratered highland materials suggests that up to 1400 m of erosion may have taken place in the highlands some of this eroded material probably remained locally burying the smaller craters later stripping of this material indicated by exposed layering and inverted topography has exhumed the smaller craters in the cratered plateau material resulting in the apparent age discrepancy determined from crater counts up to 1 0 km of material may have been removed by this later erosive event to explain the low density of ancient valley networks in the cratered plateau materials

mixed carbonate siliciclastic sequence stratigraphy of a paleogene transition zone continental shelf southeastern usa abstract the sequence stratigraphy and facies of the paleogene in the subsurface of the albemarle basin north carolina was defined using 1600 thin sections of plastic impregnated well cuttings from 24 wells wireline logs biostratigraphic data and seismic data the facies formed in the transition zone between warm subtropical and temperate conditions on a swell wave dominated open shelf exposed to major boundary current activity the shelf has a distinctive seismic profile consisting of a shallow inner shelf inner shelf break deep shelf depths in excess of 200 m and the continental slope the inner shelf was characterized by distinctive quartz sand and sandy mollusk facies inshore passing seaward into a broad wave swept abrasional shelf and then into storm influenced bryozoan echinoderm limestones to depths of several tens of meters argillaceous lime mud marl deposition was widespread across the deep shelf extending onto the inner shelf during major highstands sediment thickness trends were controlled by greater differential subsidence of crustal blocks within the albemarle basin which considerably modified but did not obliterate the effects of eustatic sea level changes in this passive margin setting five supersequences were identified on seismic and in wells each consisting of multiple regionally identifiable sequences the paleocene supersequence is dominated by widespread marl deposition reflecting shelf flooding into the late paleocene thermal maximum this warming corresponds with widespread inner shelf skeletal carbonate deposition from the late paleocene through the middle eocene the two eocene supersequences identified are dominated by bryozoan echinoderm rich carbonates that formed a seismically definable sediment buildup 50 km wide by 100 m thick across the deepest inner shelf during the lower to early middle eocene middle to upper eocene supersequence highstand sequences indicate increased progradation and greater mixing of shelf carbonates with nearshore siliciclastics likely in response to lowering sea levels and cooling climate the two oligocene supersequences identified are dominated by coarse siliciclastic sand that is heavily admixed with mollusk foraminifer dominated carbonates rapid flooding followed by extensive progradation of shallow shelf sediments in oligocene sequences reflects continued eustatic lowering driven by the onset of icehouse climatic conditions increased incision and reworking of deep shelf sediments during oligocene supersequence highstands resulted from increased ancestral gulf stream boundary current activity during icehouse times key elements controlling facies distribution through time include significant wave energy which controls the width and distribution of inner shelf facies belts through the degree of water bottom abrasion and winnowing boundary currents also are capable of large scale reworking of deep shelf sediment they also provide a mechanism for widespread inner shelf hardground development during major transgressions in addition boundary currents play a major role in stabilizing local climate by buffering seasonal temperature variations directly influencing which carbonate grain producers can thrive in this transition zone setting

quaternary tectonic faulting in the eastern united states abstract paleoseismological study of geologic features thought to result from quaternary tectonic faulting can characterize the frequencies and sizes of large prehistoric and historical earthquakes thereby improving the accuracy and precision of seismic hazard assessments greater accuracy and precision can reduce the likelihood of both underprotection and unnecessary design and construction costs published studies proposed quaternary tectonic faulting at 31 faults folds seismic zones and fields of earthquake induced liquefaction phenomena in the appalachian mountains and coastal plain of the 31 features seven are of known origin four of the seven have nontectonic origins and the other three features are liquefaction fields caused by moderate to large historical and holocene earthquakes in coastal south carolina including charleston the central virginia seismic zone and the newbury massachusetts area however the causal faults of the three liquefaction fields remain unclear charleston has the highest hazard because of large holocene earthquakes in that area but the hazard is highly uncertain because the earthquakes are uncertainly located of the 31 features the remaining 24 are of uncertain origin they require additional work before they can be clearly attributed either to quaternary tectonic faulting or to nontectonic causes of these 24 14 features most of them faults have little or no published geologic evidence of quaternary tectonic faulting that could indicate the likely occurrence of earthquakes larger than those observed historically three more features of the 24 were suggested to have had quaternary tectonic faulting but paleoseismological and other studies of them found no evidence of large prehistoric earthquakes the final seven features of uncertain origin require further examination because all seven are in or near urban areas they are the moodus seismic zone hartford connecticut dobbs ferry fault zone and mosholu fault new york city lancaster seismic zone and the epicenter of the shallow cacoosing valley earthquake lancaster and reading pennsylvania kingston fault central new jersey between new york and philadelphia and everona fault mountain run fault zone washington d c and arlington and alexandria virginia

the vlf fingerprint of elves step like and long recovery early vlf perturbations caused by powerful cg lightning em pulses 1 subionospheric vlf recordings are investigated in relation with intense cloud to ground cg lightning data lightning impacts the lower ionosphere via heating and ionization changes which produce vlf signal perturbations known as early vlf events typically early events recover in about 100 s but a small subclass does not recover for many minutes known as long recovery early events lore in this study we identify lore as a distinct category of early vlf events whose signature may occur either on its own or alongside the short lived typical early vlf event since lore onsets coincide with powerful lightning strokes of either polarity we infer that they are due to long lasting ionization changes in the uppermost d region ionosphere caused by electromagnetic pulses emitted by strong cg lightning peak currents of typically 250 ka which are also known to generate elves the lore perturbations are detected when the discharge is located within 250 km from the great circle path of a vlf transmitter receiver link the probability of occurrence increases with stroke intensity and approaches unity for discharges with peak currents 300 ka lores are nighttime phenomena that occur preferentially at least in the present regional data set during winter when strong cg discharges are more frequent and intense the evidence suggests lore as a distinct signature representing the vlf fingerprint of elves a fact which although was predicted by theory it escaped identification in the long going vlf research of lightning effects in the lower ionosphere

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve