origin distribution and alteration of asphalts at chapopote knoll southern gulf of mexico abstract following the discovery of asphalt volcanism in the campeche knolls a research cruise was carried out in 2006 to unravel the nature of the asphalt deposits at chapopote the novel results support the concept that the asphalt deposits at the seafloor in 3000 m of water depth originate from the seepage of heavy petroleum with a density slightly greater than water the released petroleum forms characteristic flow structures at the seafloor with surfaces that are ropy or rough similar to magmatic lava flows the surface structures indicate that the viscosity of the heavy petroleum rapidly increases after extrusion due to loss of volatiles consequently the heavy petroleum forms the observed asphalt deposit and solidifies detailed survey with a remotely operated vehicle revealed that the asphalts are subject to sequential alterations e g volume reduction leading to the formation of visible cracks in the asphalt surface followed by fragmentation of the entire deposit while relatively fresh asphalt samples were gooey and sticky older fragmented pieces were found to be brittle without residual stickiness furthermore there is evidence for petroleum seepage from below the asphalt deposits leading to local up doming and sometimes to whip shaped extrusions extensive mapping by tv guided tools of chapopote asphalt volcano indicates that the main asphalt deposits occur at the south western rim that borders a central crater like depression the most recent asphalt deposit at chapopote is the main asphalt field covering an area of 2000 m2 asphalt volcanism is distinct from oil and gas seepage previously described in the gulf of mexico and elsewhere because it is characterized by episodic intrusions of semi solid hydrocarbons that spread laterally over a substantial area and produce structures with significant vertical relief as chapopote occurs at the crest of a salt structure it is inferred that asphalt volcanism is a secondary result of salt tectonism

planetary dune analogues a special issue on integrating models remote sensing and field data this article reports on the special issue of earth surface processes and landforms dedicated to planetary dune analogues and the advances that have been made through the integration of remote sensing and terrestrial field data to better model and understand aeolian systems the 11 articles presented demonstrate a spectrum of analytical techniques that are employed to investigate ripples dunes draa and ergs across a variety of spatial and temporal scales nine of the papers involve innovative research about aeolian bedforms and processes while the final two papers are examples of how vast quantities of data may be organized and scrutinized using a giscience approach based on these 11 papers and the many abstracts archived in a series of three planetary dunes workshops at the lunar planetary institute http www lpi usra edu publications abstracts shtml lpi contributions 1403 1552 and 1673 it is evident that there exists diverse and complementary approaches to the comparative study of landforms and processes for terrestrial and extra terrestrial aeolian landscapes that is driven by a vibrant international community of scientists and educators that engage in the cross fertilization of ideas copyright 2014 john wiley sons ltd

geologic framework of upper miocene and pliocene gas plays of the macuspana basin southeastern mexico this integrated study provides a geological and geochemical framework for upper miocene and pliocene siliciclastic gas plays in the macuspana basin structural controls for the plays are deep seated faults that tap mesozoic thermogenic gas sources areas of intense shale diapirism and folding and areas with structural inversion that could enhance trapping and reservoir productivity early neogene thrusting south of the basin triggered evacuation of oligocene shale along northwest dipping listric faults in the eastern and southeastern basin margin these faults are associated with large scale rollover structures and thick 500 m upper miocene shoreface and wave dominated deltaic complexes a second phase of extension in the early pliocene formed a set of broad southeast dipping listric faults in the western basin controlling thick accumulations of stacked pliocene shoreface deposits trap formation and enhancement in the southern basin margin are linked to late miocene to pliocene inversion the primary stratigraphic controls on play occurrence in the upper miocene in the onshore part of the basin are the regional facies distribution of northwest prograding shoreface and wave dominated deltaic systems there was a shift in pliocene sedimentation from the southeast to the west and northwest parts of the basin where thick successions of aggradational shoreface and wave dominated deltaic deposits accumulated in depocenters defined by shale evacuation along growth faults valley fill deposits in both the upper miocene and pliocene resulted from shortlived periods of base level change induced by either uplift on the southern basin margin or eustasy the offshore part of the basin is inferred to consist of deep water turbidite deposits that formed downdip westward of a hypothesized mixed clastic carbonate prograding complex from the yucatan platform three petroleum systems mesozoic paleogene lower neogene and upper miocene pliocene contributed to the hydrocarbon accumulations and hydrocarbon generation and migration in the basin principal upper jurassic lower cretaceous source rocks generated wet thermogenic gases and oil secondary lower tertiary source rocks generated dominantly dry biogenic gases mixtures of the two gas types are common numerous deep seated growth faults and faults serve as pathways for mesozoic sourced hydrocarbons surface seeps and abundant gas shows suggest that hydrocarbons are being generated today

anomalies in geomagnetic variations on peninsular india near palk strait anomalies in transient geomagnetic variations have been previously studied using data from five permanent observatories in the peninsular india the results from the three observatories falling under the equatorial electrojet showed the presence of a strong current concentration between india and sri lanka island the currents seem to flow at the depth of the crust or upper mantle these findings have been confirmed hereby by collecting data from an array of magnetometers we associate the channelling to the presence of a geological conductor between india and sri lanka island

orbital observations of contemporary dune activity in endeavor crater meridiani planum mars 1 although aeolian landforms are pervasive on mars evidence for contemporary activity has been limited the next major campaign for the mars exploration rover opportunity is the investigation of the 20 km diameter endeavor crater 6 km to southeast of the rover s position as of december 2010 we present evidence from orbital imagery that eight aeolian bed forms 14 000 m2 in endeavor crater have been active within the past decade 2001 2009 at a spatial scale that should be directly observable by opportunity from the crater rim two dunes appear to show translational migration 10 20 m but all dunes indicate erosion to be the dominant process with up to 100 sediment removal thermophysical properties of these dunes are consistent with very fine to fine sand sizes the particle sizes most easily moved by the martian atmosphere the dunes that show the most surface change have a rippled appearance without well defined slip faces based on their morphology elliptical shape we classify them as dome dunes mesoscale atmospheric modeling is employed to provide insight into the atmospheric forcing of this aeolian system the major wind regimes from modeling are consistent with observations of wind streaks sand streamers ripples and slip faces of regional dune fields although modeled wind speeds are insufficient to move sand the translation and erosion of these dunes constitutes the largest contemporary movement of sand sized sediment reported on mars to date and demonstrates that endeavor crater has been subject to wind profiles exceeding the threshold velocity at the surface daily seasonally and or episodically in the recent past

petroleum degradation and associated microbial signatures at the chapopote asphalt volcano southern gulf of mexico abstract at the chapopote knoll in the southern gulf of mexico deposits of asphalt provide the substrate for a prolific cold seep ecosystem extensively colonized by chemosynthetic communities this study investigates microbial life and associated biological processes within the asphalts and surrounding oil impregnated sediments by analysis of intact polar membrane lipids ipls petroleum hydrocarbons and stable carbon isotopic compositions 13c of hydrocarbon gases asphalt samples are lightly to heavily biodegraded suggesting that petroleum derived hydrocarbons serve as substrates for the chemosynthetic communities accordingly detection of bacterial diester and diether phospholipids in asphalt samples containing finely dispersed gas hydrate suggests the presence of hydrocarbon degrading bacteria biological methanogenesis contributes a substantial fraction to the methane captured as hydrate in the shallow asphalt deposits evidenced by significant depletion in 13c relative to background thermogenic methane in sediments petroleum migrating from the subsurface stimulates both methanogenesis and methanotrophy at a sulfate methane transition zone 6 7 m below the seafloor in this zone microbial ipls are dominated by archaeal phosphohydroxyarchaeols and archaeal diglycosidic diethers and tetraethers bacterial ipls dominate surface sediments that are impregnated by severely biodegraded oil in the sulfate reduction zone diagnostic ipls indicate that sulfate reducing bacteria srb play an important role in petroleum degradation a diverse mixture of phosphohydroxyarchaeols and mixed phospho and diglycosidic archaeal tetraethers in shallow oil impregnated sediments point to the presence of anaerobic methane oxidizing anme 2 and anme 1 archaea respectively or methanogens archaeal ipls increase in relative abundance with increasing sediment depth and decreasing sulfate concentrations accompanied by a shift of archaeol based to tetraether based archaeal ipls the latter shift is suggested to be indicative of a community shift from anme 2 and or methanogenic archaea in shallower sediments to anme 1 methanogenic archaea and possibly benthic archaea in deeper sediments

cold seeps at the salt front in the lower congo basin ii the impact of spatial and temporal evolution of salt tectonics on hydrocarbon seepage abstract this study investigates the distribution and evolution of seafloor seepage in the vicinity of the salt front i e the seaward boundary of salt induced deformation in the lower congo basin lcb seafloor topography backscatter data and tv sled observations indicate active fluid seepage from the seafloor directly at the salt front whereas suspected seepage sites appear to be inactive at a distance of 10 km landward of the deformation front high resolution multichannel seismic data give detailed information on the structural development of the area and its influence on the activity of individual seeps during the geologic evolution of the salt front region the unimpeded migration of gas from fan deposits along sedimentary strata towards the base of the gas hydrate stability zone within topographic ridges associated with relatively young salt tectonic deformation facilitates seafloor seepage at the salt front bright and flat spots within sedimentary successions suggest geological trapping of gas on the flanks of mature salt structures in the eastern part of the study area onlap structures associated with fan deposits which were formed after the onset of salt tectonic deformation represent potential traps for gas which may hinder gas migration towards seafloor seeps faults related to the thrusting of salt bodies seawards also disrupt along strata gas migration pathways additionally the development of an effective gas hydrate seal after the cessation of active salt induced uplift and the near surface location of salt bodies may hamper or prohibit seafloor seepage in areas of advanced salt tectonic deformation this process of seaward shifting active seafloor seepage may propagate as seaward migrating deformation affects congo fan deposits on the abyssal plain these observations of the influence of the geologic evolution of the salt front area on seafloor seepage allows for a characterization of the large variety of hydrocarbon seepage activity throughout this compressional tectonic setting

marine geophysical study of the comorin ridge north central indian basin marine geophysical data are used to interpret the continental margin structure south of india and west of sri lanka in the northern central indian basin free air and isostatic anomaly maps are presented they show the prominent indian ocean gravity low with values more negative than 100 mgal south west of sri lanka a steep gradient in the free air and isostatic anomaly forms a nnw sse trending line extending south and striking parallel to the southwest coast of india this line marks the eastern boundary of a topographic and basement high here named the comorin ridge which is also clearly seen on a sediment isopach map the ridge seems to act as a barrier to the passage of ganges cone sediments to the west a comparison of the eastern landward edge of the comorin ridge with similar structures of other passive continental margins such as those off southern south africa agulhas fracture zone off the falkland plateau and off western norway is made it is suggested that the eastern edge of the comorin ridge may mark a significant structural crustal boundary

inverse maximum gross bedform normal transport 2 application to a dune field in ganges chasma mars and comparison with hirise repeat imagery and mrams abstract inverse maximum gross bedform normal transport imgbnt analysis has been applied to context camera ctx images of the largest dune field in ganges chasma on mars the dune field was selected for its position in a likely complex multi directional wind regime results indicate that four main winds are responsible for simultaneous construction of the dune field including along chasma winds from the ese winds blowing down a nearby re entrant from the ne winds blowing down the adjacent chasma wall from the nw and chasma floor winds from the sw each wind represents a transport vector that dominates dune morphology at its respective edge of the dune field such that the central axis of the dune field reflects the convergence of the three most prominent winds ese nw and sw the mars regional atmospheric modeling system mrams was run at twelve times throughout the martian year to provide context for the local wind patterns potential sand fluxes calculated from mrams output show that three major air flows from the ene e nne ne and nnw n converge near the location of the dune field these flows likely correspond to the ese ne and nw winds identified from imgbnt analysis respectively mrams output shows that the flows with major northerly components are produced by larger scale hadley return flow constructively combining with nighttime downslope winds the flow with a major easterly component is likely produced by equatorial easterly trade winds constructively combining with the diurnal tide and or local topography although the model correctly predicts the major elements of the local wind pattern some aspects are either over or underrepresented demonstrating the value of using aeolian morphological analysis to conclusively constrain the major sand moving winds on mars overlapping high resolution imaging experiment hirise images of barchanoid dunes at the northernmost edge of the dune field indicate that these dunes are currently migrating southward at 5 m mars year 2 6 m earth year the direction of migration is consistent with both mrams predictions in this location and the nw ne winds found from imgbnt analysis dune morphology suggests that sand in the northwestern part of the dune field is likely to be derived from the adjacent chasma wall to the north and northwest and sand in the southeastern part of the dune field was probably transported from farther east along the main chasma floor

a conceptual model for hydrocarbon accumulation and seepage processes around chapopote asphalt site southern gulf of mexico from high resolution seismic point of view 1 as part of the german r v meteor m67 2 expedition in 2006 to the southern gulf of mexico a set of 2d high resolution seismic profiles was acquired across the chapopote knoll to study seafloor asphalt occurrences on the basis of regional seismostratigraphic studies and dsdp drilling a more highly reflective coarse grained sediment unit of late miocene age is identified as a potential shallow hydrocarbon reservoir although a unit of that age would typically be buried by pliocene and pleistocene sediment cover at chapopote local salt tectonism has highly elevated the structure since the late miocene and the miocene reservoir is locally above present day regional datum the elevation resulted in a thin 100 200 m fine grained sediment cover on the crest of the knoll above the reservoir because oil and gas production can be expected at depth in jurassic cretaceous and tertiary source rocks the presence of high amplitude reflector packages within the reservoir unit is interpreted as an evidence of hydrocarbons this is variously supported by observations of crosscutting reflectors polarity reversal and drops in instantaneous frequency the thin seal above the reservoir unit facilitates leakage of trapped hydrocarbons hydrocarbons apparently invaded into the seal sediments in the wider vicinity around the crest of the knoll even extending beyond the area where seafloor asphalt is known the asphalt site thus may be a currently active spot while the rest of the crest may be temporarily sealed by solid phase hydrocarbons we propose that a shallow large reservoir with deeply sourced relatively heavy petroleum is principally responsible for the formation of asphalts on the seafloor

longitudinal dunes on mars relation to current wind regimes longitudinal dunes are extremely rare on mars but constitute a substantial fraction of terrestrial desert dunes we report finding isolated examples of longitudinal dunes on mars and relate their occurrence to expected sand transport regimes terrestrial longitudinal dunes form in bimodal and multimodal transport regimes general circulation models and streak data indicate that bimodal and multimodal transport of sand should be very rare on mars thus the dearth of longitudinal dunes on mars is consistent with their apparent formation conditions on earth

aeolian processes and dune morphology in gale crater abstract datasets at resolutions many times greater than previously available were used to study aeolian features within gale crater high resolution thermal inertia data allowed for detailed particle size estimation with the data sufficient to resolve dunefields a wide range of grain sizes have now been identified in the gale crater dunefields ranging from medium to very coarse sand high resolution imaging science experiment hirise and themis vis data allowed for detailed analysis of the dune morphology and slip faces which shows that the dunes have responded to topographic influences on prevailing wind directions under a present day wind regime this result was corroborated by a regional mesoscale model for the crater under dust storm conditions the central mound and smaller scale crater floor topography has altered the prevailing wind regime and dune patterns aeolian activity has thus played and continues to play an important role in shaping many of the present surface features of gale crater the arrival of a future lander mission such as the mars science laboratory would be able to sample these surface features directly and add a wealth of data to the understanding of gale crater

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

magnetovariational study over a seismically active area in the deccan trap province of western india this paper presents the results of a magnetovariational study undertaken over a basalt covered region of western india which has been experiencing a swarm of seismic activity since early 1986 the most striking feature of the transient variations is the anomalous enhancement of the east west y component at stations bounding the seismically active belt from the nature of the horizontal transfer functions and the anomalous induction arrows it is inferred that this behaviour is related to the presence of a resistive body embedded in a north south oriented conductive belt consistent with an evolutionary model of deccan volcanism and other geophysical data it is suggested that the central resistive block coincident with the concentrated belt of earthquake epicentres represents either a dormant volcanic plug or a plutonic body rooted in upwarped conducting mantle to account for the phase relationship between the anomalous y variations and the normal north south x variations it is proposed that the upwarped asthenosphere with its associated high geothermal anomaly acts as a conducting path to channel induced current from the region of the cambay triple junction located towards the northwest of the array the existence of the strong induced currents in the region of the triple junction conforms with the induction arrow pattern observed at the array stations

dune morphology sand transport pathways and possible source areas in east thaumasia region mars an aeolian system located in aonia terra eastern thaumasia region consists of six dark dune fields the dune pattern suggests an organized extended sand transport system which is characterized by the presence of long sand corridors the latter connects the different ergs with potential sources the sand stored in the ergs is provided by layered materials exposed in pits and crater walls and by the ergs themselves most of the sand converges from the marginal dune fields into the central erg c the latter develops in an area of convergence of at least three different winds from the southwest the northeast and the northwest the northwesterly flows seem to postdate the other winds as suggested by the development of a complex dune pattern in the western portion of the erg c representing a successive episode of aeolian construction collectively such complex dune patterns show how dune fields could record major changes in the wind regimes of mars

the rate of granule ripple movement on earth and mars abstract the rate of movement for 3 and 10 cm high granule ripples was documented in september of 2006 at great sand dunes national park and preserve during a particularly strong wind event impact creep induced by saltating sand caused 24 granules min 1 to cross each cm of crest length during wind that averaged 9 m s 1 at a height well above 1 m which is substantially larger than the threshold for saltation of sand extension of this documented granule movement rate to mars suggests that a 25 cm high granule ripple should require from hundreds to thousands of earth years to move 1 cm under present atmospheric conditions

shallow sediment deformation styles in north western campeche knolls gulf of mexico and their controls on the occurrence of hydrocarbon seepage during german r v meteor m67 2 expedition to campeche knolls southern gulf of mexico a set of 2d high resolution seismic data was acquired to study the near surface sediment structure and its relationship with hydrocarbon seepages in this salt province the comprehensive survey covered 20 individual bathymetric highs or ridges and identified three principle structural types passive type chaopopte type and asymmetric flap type the first type is the result of passive diapirism whereas the latter two were initialized by a regional compressional event in the miocene but are later differently modified by salt tectonism chapopote type structures appear as symmetrical domes with uplifted coarse grained miocene sediments in their cores and rather thin syn kinematic sediments covering the crests asymmetric flap type structures are also first folded as domes or ridges but one flap later subsided together with salt evacuation resulting in single uplifted monoclines with the coarse grained pre kinematic sediments as reservoir units both structural types can focus and accumulate hydrocarbons the geometries of the structures suggest that hydrocarbons are accumulated in the center of the chapopote type structures and in the subsided flaps of the asymmetric flap type structures hydrocarbon leakage from these thinly sealed reservoirs is regarded as the principle mechanism for the seepage in the study area and accordingly the most seepage prone positions are above these reservoirs the seep locations suggested by analysis of sea surface oil slick images of sar satellite data are also examined in this study these independently derived seep locations confirm the seepage prone positions to be above the shallow buried reservoirs this study suggest that the shallow sediment structures control the distribution of the hydrocarbon seeps of the north western campeche knolls although the hydrocarbons are sourced from the greater depth

spectral and petrologic analyses of basaltic sands in ka u desert hawaii implications for the dark dunes on mars dark aeolian bedforms on mars are thought to consist of volcanic materials due to their mineral assemblages which are common to basalts however the sediment source is still debated and needs further affirmation basaltic dunes on earth are rare and can only be found in a few places including new zealand iceland the western usa peru and hawaii these dunes composed of volcaniclastic sediments are promising analogues for providing further insights into the assumed basaltic sand dunes on mars in our study we use basaltic dunes sands collected in hawaii s ka u desert which are especially interesting for addressing the source of martian dunes because of the co occurrence of active volcanic processes and dune development for these dunes we could prove that their material has been derived from airfall ashes from phreatomagmatic eruptions of kilaulea and reworked lava basaltic dunes sand from arizona builds a second set of terrestrial analogue samples in our study these sands have been collected from aeolian bedforms that are composed of reworked volcanic ash erupted from nearby sinter cones spectral analyses of the terrestrial samples show that the dune sands are enriched in pyroxene and olivine a basaltic composition similar to that of the martian dark dunes microprobe analyses show that the terrestrial sands are dominated by olivine pyroxene plagioclase and glasses resulting from the volcanic source of these aeolian sediments this result is consistent with modal mineralogy modeling of martian dunes sands these correlations prove the hypothesis of a similar origin of the martian and terrestrial dune sands consistent with reworked volcanic ash and lava

the influence of local topography for wind direction on mars two examples of dune fields in crater basins in this work we perform an analysis of large dark dunes within moreux crater and herschel crater on mars using high resolution imaging science experiment hirise and context camera ctx data sets these data allow us to conduct a detailed analysis of dune morphology and slip faces concluding that the studied dune fields are influenced by topographically controlled complex wind directions our morphological analysis reveals that inside moreux crater in particular the topographic setting dominates the wind flow direction leading to the development of a sand transport pathway encircling the central peak of the crater the dune fields in herschel crater are also affected by winds controlled by variable topography as suggested by the presence of complex dunes and dune fields our analysis indicate that the studied dune systems is not the result of paleo wind regimes furthermore we perform thermal inertia measurements using thermal emission spectrometer tes data which indicate that the studied dune fields consist of medium sand 250 500 mm in diameter

cold seeps at the salt front in the lower congo basin i current methane accumulation and active seepage abstract active high intensity gas seepage is documented for the first time at the seaward edge of the salt occurrence in the southern lower congo basin microbial methane release from the seafloor occurs on the crests of two 800 m high ridges formed by fault propagation folding intense uplift is documented since the end of the miocene by distinct onlapping reflections on the landward flank of these ridges a paleo pockmark structure suggests an onset of seepage coincident with this deformation period high resolution seismic imaging reveals methane migration along strata from oligocene miocene fan deposits towards the ridge crests where large gas accumulations form beneath a discontinuous bottom simulating reflection bsr detailed mapping revealed that free gas and gas hydrate occurrences below and above the base of the gas hydrate stability zone are closely linked to sedimentary strata in the flanks of topographic ridges gas transport through the gas hydrate stability zone originates from the shallowest area of the bsr directly beneath the seafloor seep sites suggesting pressure controlled venting these sites represent the most seaward salt related gas seepage features documented in the area and illustrate the initiation of long lasting seepage at the front of an area of compressional tectonics at a passive continental margin

star and linear dunes on mars abstract a field containing 11 star and incipient star dunes occurs on mars at 8 8 s 270 9 w examples of linear dunes are found in a crater at 59 4 s 343 w while rare dune varieties that form in bi and multidirectional wind regimes are not absent from the surface of mars the occurrence of both of these dune fields offers new insight into the nature of martian wind conditions and sand supply the linear dunes appear to have formed through modification of a formerly transverse aeolian deposit suggesting a relatively recent change in local wind direction the 11 dunes in the star dune locality show a progressive change from barchan to star form as each successive dune has traveled up into a valley into a more complex wind regime the star dunes corroborate the model of n lancaster 1989 progr physical geogr 13 67 91 1989 sedimentology 36 273 289 for the formation of star dunes by projection of transverse dunes into a complex topographically influenced wind regime the star dunes have dark streaks emanating from them providing evidence that the dunes were active at or near the time the relevant image was obtained by the viking 1 orbiter in 1978 the star and linear dunes described here are located in different regions on the martian surface unlike most star and linear dunes on earth both martian examples are isolated occurrences neither is part of a major sand sea previously published mars general circulation model results suggest that the region in which the linear done field occurs should be a bimodal wind regime while the region in which the star dunes occur should be unimodal the star dunes are probably the result of localized complication of the wind regime owing to topographic confinement of the dunes local topographic influence on wind regime is also evident in the linear dune field as there are transverse dunes in close proximity to the linear dunes and their occurrence is best explained by funneling of wind through a topographic gap in the upwind crater wall

flume experiments on the alignment of transverse oblique and longitudinal dunes in directionally varying flows for more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow whereas others are parallel or oblique to flow this problem of bedform alignment was studied experimentally using subaqueous dunes on a 3 6 m diameter sand covered turntable on the floor of a 4 m wide flume in each experiment two flow directions relative to the bed were produced by alternating the turntable between two orientations the turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms the resulting bedforms were in equilibrium with the time averaged conditions of the bimodal flows dune alignment was studied for five divergence angles the angle between the two flow directions 45 67 5 90 112 5 and 135 the flow depth during all experiments was approximately 30 cm mean velocity was approximately 50 cm s 1 and mean grain diameter was 0 6 mm each experiment continued for 30 75 min during which time the flume flow was steady and the turntable position changed every 2 min at the end of each experiment water was slowly drained from the flume and dune alignment was measured transverse dunes defined relative to the resultant transport direction were created when the divergence angle was 45 and 67 5 and longitudinal dunes were created when the divergence angle was 135 at intermediate divergence angles dunes with both orientations were produced but transverse dunes were dominant at 90 and longitudinal dunes were dominant at 112 5 one experiment was conducted with a divergence angle of 135 and with unequal amounts of transport in the two flow directions this was achieved by changing the orientation of the turntable at unequal time intervals thereby causing the amount of transport to be unequal in the two directions the dunes formed during this experiment were oblique to the resultant transport direction these experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments in both sets of experiments the bedforms developed with the orientation having the maximum gross bedform normal transport the orientation at which the sum of the bedform normal components of the two transport vectors reaches its maximum value in other words the bedforms develop with an orientation that is as transverse as possible to the two flows in those cases where the two flows diverge by more than 90 and transport equal amounts of sand bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors although such bedforms have been defined by previous work as longitudinal bedforms they are intrinsically the same kind of bedform as transverse bedforms

induction models of southern india and the effect of off shore geology abstract simple numerical tests based on thin sheet modelling are used to define the conductors most probably responsible for current channelling in the region including southern india a combination of crustal conductors located in the indo ceylon graben and underneath the comorin ridge best reproduces the observations at periods of 50 100 min in so far as channelling is concerned daytime variations do not help to define the location of conductors any better than night time data and may thus be ignored

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

mixed gas hydrate structures at the chapopote knoll southern gulf of mexico abstract in underwater hydrocarbon seepage environments gas hydrates are considered to play a significant role as shallow gas reservoirs and buffers for light hydrocarbon expulsion here we report on mixed hydrate structures from the chapopote knoll in the southern gulf of mexico and discuss several options on how a mixture of structure i si and structure ii sii gas hydrate may occur in nature locally resolving microscopic methods are needed to characterize the coexistence of different hydrate structures at geological hydrate deposits we used raman spectroscopy x ray diffraction and gas chromatography for our investigations gas hydrates were found within the matrix and pores of the asphalts extruded at the seafloor two of the three hydrate pieces investigated comprised only si formed mostly from methane in contrast one piece comprised an intimate mixture of both si and sii with sii representing ca 25 wt and si ca 75 wt of the hydrate present the two structures were closely associated within individual grain agglomerates the crystallites of sii were significantly larger than of si suggesting differences in the nucleation density or different crystallite ages the structural coexistence may be a result of one or more processes i de mixing into two hydrate structures during the growth from the gas phase which provides an additional degree of freedom for lowering the free energy in the system ii fractionated crystallization with a subsequently changing molecular composition iii crystallization from separated gas bubbles with different hydrocarbon compositions and water and iv partial transformation from sii to si after hydrate nucleation ceasing when a thermodynamically stable state was reached the presented work will affect future assessments of natural hydrate deposits at thermogenic hydrocarbon systems as it shows that both hydrate types i and ii can be present at a certain geological site and may provide a lingering strength to the system if conditions fall below the si stability limit this suggests that present worldwide hydrate occurrences are likely to be underestimated

variations in wind velocity and sand transport on the windward flanks of desert sand dunes the magnitudes of increases in wind velocity or speed up factors have been measured on the windward flanks of transverse and linear dunes of varying height on transverse dunes velocity speed up varied with dune shape and height for linear dunes speed up factors varied principally with wind direction relative to the dune with dune shape and dune height the main effect of velocity speed up on the windward flanks of dunes is to increase potential sand transport rates considerably in crestal areas this is greatest for large dunes with winds of moderate velocity blowing at a large angle to the dune changing ratios of base to crest sand transport rates on transverse dunes tend to reduce dune steepness as overall wind velocities increase on linear dunes the tendency for crestal lowering is counteracted by deposition in this area when winds reverse in a bi directional wind regime

geomagnetic variation anomalies in peninsular india summary geomagnetic substorms recorded by an array of magnetometers over peninsular india have been analysed to investigate the subsurface electric configuration of the area the study considered only night time events when the external inducing field is uniform over the indian peninsula and the conventional interpretational techniques of geomagnetic deep sounding can be readily applied contour maps of fourier transform amplitudes and phases along with real and quadrature parkinson arrows are presented their features reveal a complex anomaly pattern the observed anomalies can be classified into i southern peninsular anomalies ii palk sirait anomalies iii pondicherry rift anomalies and iv anomalies in the central region a large scale induction process seems to be disturbed by localized perturbations the prominent anomaly observed over the southern tip seems to have a direct relevance to the tectonic setting of the indian ocean and adjoining areas

acoustic imaging of gas hydrate and free gas at the storegga slide 1 analysis of p wave velocities of an ocean bottom cable obc data set demonstrates the existence of gas hydrates and free gas on the northern flank of the storegga slide the distribution and concentration of gas hydrates and free gas show significant variation over the length of the obc average gas hydrate saturation of pore space is 5 when modeled by effective medium theory with hydrates as a sediment frame component average gas saturation is 0 45 assuming homogeneous distribution the bottom simulating reflector bsr is generally identified as termination of enhanced reflection but in some places appears as a reflection proper amplitude anomalies related to the bsr are primarily caused by the gas and not the hydrates the gas hydrates at the storegga slide develop from gas rich fluids migrating into the gas hydrate stability zone ghsz from the sediments below development of polygonal faults and the related expulsion of formation water might drive the fluid flow in the area the physical and geological properties of the sediments control the distribution and concentration of gas which migrates predominantly along strata rather than along the base of the ghsz this migration mechanism controls the flux of gas rich fluids into the ghsz and hence the distribution of gas hydrates and the variation in gas hydrate concentration

aeolian dunes as ground truth for atmospheric modeling on mars 1 martian aeolian dunes preserve a record of atmosphere surface interaction on a variety of scales serving as ground truth for both global climate models gcms and mesoscale climate models such as the mars regional atmospheric modeling system mrams we hypothesize that the location of dune fields expressed globally by geographic distribution and locally by dune centroid azimuth dca may record the long term integration of atmospheric activity across a broad area preserving gcm scale atmospheric trends in contrast individual dune morphology as expressed in slipface orientation sf may be more sensitive to localized variations in circulation preserving topographically controlled mesoscale trends we test this hypothesis by comparing the geographic distribution dca and sf of dunes with output from the ames mars gcm and at a local study site with output from mrams when compared to the gcm 1 dunes generally lie adjacent to areas with strongest winds 2 dca agrees fairly well with gcm modeled wind directions in smooth floored craters and 3 sf does not agree well with gcm modeled wind directions when compared to mrams modeled winds at our study site 1 dca generally coincides with the part of the crater where modeled mean winds are weak and 2 sfs are consistent with some weak topographically influenced modeled winds we conclude that 1 geographic distribution may be valuable as ground truth for gcms 2 dca may be useful as ground truth for both gcm and mesoscale models and 3 sf may be useful as ground truth for mesoscale models

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

salt formation associated with sub surface boiling and supercritical water abstract laboratory experiments have demonstrated that supercritical water has extremely low solubility for normal sea salts this fact opens up the possibility for the precipitation of salt from seawater that circulates in faults and fractures close to a heat source in tectonically active basins typically extensional pre rifts and rift settings seawater attains supercritical conditions at depths exceeding 2800 m corresponding to a pressure of 300 bars and temperatures above 405 c salts may also precipitate by the boiling of seawater in sub surface or submarine settings this is demonstrated by a simple laboratory experiment the theoretical basis for the precipitation of salts from seawater attaining supercritical condition has been examined by molecular modelling these processes of salt precipitation constitute a new approach to the geological understanding of salt deposits and two regions are selected to examine whether salt may have deposited under such hydrothermal conditions today the atlantis ii deep in the red sea marine setting and lake asale dallol ethiopia continental setting

a novel method to measure calcium carbonate with portable x ray fluorescence instrumentation and its application to gulf of mexico surficial sediments abstract a novel rapid low cost non destructive and reliable technique was developed to simultaneously measure calcium carbonate caco3 and trace element concentrations in sediments with a portable x ray fluorescence pxrf analyzer and applied to 27 samples of surficial sediments collected from the yucatan continental shelf 1200 m water depth of the gulf of mexico this technique is based on calculation of authigenic calcium caauth from the total ca measured with the pxrf results obtained with the pxrf showed a very high and highly significant correlation r 0 99 p

aeolian processes in proctor crater on mars mesoscale modeling of dune forming winds 1 both atmospheric modeling and spacecraft imagery of mars are now of sufficient quality that the two can be used in conjunction to acquire an understanding of regional and local scale aeolian processes on mars we apply a mesoscale atmospheric model adapted for use on mars the mars mm5 to proctor crater a 150 km diameter crater in the southern highlands proctor crater contains numerous aeolian features that indicate wind direction including a large dark dune field with reversing transverse and star dunes containing three different slipface orientations small and older bright bedforms that are most likely transverse granule ripples and seasonally erased dust devil tracks results from model runs spanning a martian year with a horizontal grid spacing of 10 km predict winds aligned with two of the three dune slipfaces as well as spring and summer winds matching the dust devil track orientations the primary most prevalent dune slipface orientation corresponds to a fall and winter westerly wind created by geostrophic forces the tertiary dune slipface orientation is caused by spring and summer evening katabatic flows down the eastern rim of the crater influencing only the eastern portion of the crater floor the dunes are trapped in the crater because the tertiary winds enhanced by topography counter transport from the oppositely oriented primary winds which may have originally carried sand into the crater the dust devil tracks are caused by light spring and summer westerly winds during the early afternoon caused by planetary rotation the secondary dune slipface orientation is not predicted by model results from either the mars mm5 or the geophysical fluid dynamics laboratory mars general circulation model the reason for this is not clear and the wind circulation pattern that creates this dune slipface is not well constrained the mars mm5 model runs do not predict stresses above the saltation threshold for dune sand of the appropriate size and composition as with previous work the calculated wind velocities are too low which may be caused by too large of a grid spacing

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

present day aeolian activity in herschel crater mars abstract in this report we show evidence for ripple and dune migration in herschel crater on mars we estimate an average dune migration of 0 8 m and a minimum ripple migration of 1 1 m in a time span of 3 7 earth years these dunes and ripples are mainly shaped by prevailing winds coming from the north however we also report the presence of secondary winds which elongate the barchans horns such a complex wind scenario is likely caused by the influence of winds blowing off the western crater rim as suggested by the mars regional atmospheric modeling system mrams an atmospheric mesoscale model a multi directional wind regime at the local scale is also supported by the observed bimodal distribution of the ripple trends for the first time a survey integrating the assessment of dune and ripple migration is presented showing how dune topography can influence the migration patterns of ripples and how underlying topography appears to control the rates of dune migration

conceptual modeling of onshore hydrocarbon seep occurrence in the dezful embayment sw iran petroleum and gas seeps on the ground surface are direct indicators of accumulations of hydrocarbons in the subsurface and could reflect the migration of hydrocarbons in a sedimentary basin quantitative analyses of the spatial pattern of hydrocarbon seeps and their spatial associations with geological features could aid in deducing geological controls on their occurrence in this study the fry analysis was applied to study the spatial pattern of mapped hydrocarbon seeps whereas spatial association analyses were implemented to quantify the spatial association of mapped seeps and their alteration products with geological features the spatial pattern analysis of hydrocarbon seeps showed that oil seeps followed prominent nw se and ne sw trends while gas seeps followed nw se and n s trends suggesting that nne ssw and nw se fractures are possible migration pathways for hydrocarbons to reach the surface the results of the spatial association analysis illustrated strong positive spatial associations of oil and gas seeps with the gachsaran and the mishan formations implying upward migration of hydrocarbons through permeable micro fractures and micro pores in their strata a conceptual model has proposed for the occurrence of onshore hydrocarbon seeps in the dezful embayment

amalgamated accumulations resulting from climatic and eustatic changes akchar erg mauritania the akchar erg of the sahara of western mauritania shows a morphology and stratigraphy that can be recognized as the amalgamation of late pleistocene and holocene deposits that reflect eustatic and climatic events mapping trenching and dating by 14c methods and artefacts show that the prominent complex linear dunes draas of the akchar erg are actually composite features showing at least three constructional and two destructional phases the constructional phases are represented by three convex up layers i a modern veneer moulded into superimposed crescentic dunes which partially mantle the larger linear bedforms ii a middle partly root turbated sand deposited sometime during the last 4000 years and iii a core of linear dune sand formed during the last glacial period 13 000 20 000 yr bp which today shows relict relief intense root turbation and pedogenesis these constructional phases are separated by super bounding surfaces that coincide with erg destructional phases surface 2 bounds the middle aeolian sand and is marked by a lag surface of small granules surface 1 is a very prominent surface with an abundance of neolithic artefacts and represents stabilization of the linear dunes during the humid interglacial period 4000 11 000 yr bp interdraa deposits originated during the interglacial period and consist of continental lacustrine limestones and sandstones humic sands deposited in marshes and sabkhas on the coast the sabkhas originated during interglacial highstand of sea level when interdraa areas were marine embayments and subsequently dried during regression the draa and interdraa sequences therefore in spite of being adjacent facies actually represent different events and were not formed simultaneously the upwind sand sheet margin of the akchar erg shows exposures of the middle and core aeolian sands which were previously protected from deflation by vegetation being progressively cannibilized in the current phase of erg construction and revealing a crystalline basement rock in this proximal area conditions are not favourable for the incorporation of these aeolian accumulations into the stratigraphic record

morphological and sedimentary characteristics of dome dunes in the northeastern qaidam basin china abstract oval dome dunes which lack a slipface represent a specific phase of barchan dune evolution that has undergone distinctive morphodynamic processes in the northeastern qaidam basin china we measured the morphological parameters of 60 dome dunes by means of real time kinematic gps the dome dunes had an oval plan view and an asymmetrical side view with mean lengths of 14 49 and 13 26 m for the long and short axes respectively with mean windward and leeward slopes of 4 56 and 5 07 respectively dune heights ranged between 0 12 and 0 91 m and averaged 0 52 m by examining the characteristics of the dune sediments the internal sedimentary structures and regional wind regimes we found that local alluvial and fluvial sediments appear to provide the necessary materials for the dome dunes and that the dunes evolved from sand patches under a variable gentle winter wind according to our results and the andreotti saturation length theory we estimated the lengths at which the dome dunes disperse or begin to evolve into barchan dunes this knowledge will enhance our understanding of dome dune morphodynamic processes and improve numerical simulations of dune evolution

dune migration and slip face advancement in the rabe crater dune field mars 1 eight overlapping images of a dune slip face in rabe crater 35 e 44 s from the mars global surveyor mars orbiter camera show changes interpreted to be multiple grainflow events that would indicate present day sand saltation and dune migration new occurrences of these features appear sporadically throughout late southern summer and early fall and then no further changes occur throughout winter by the following summer the pattern of old streaks had been almost completely covered by new dark streaks assuming that this activity is typical from year to year migration rates are estimated to be on the order of 1 2 cm per martian year produced by south to southeasterly winds that blow mostly during the southern spring and early summer this slow migration rate is consistent with a present day sediment state that is either transport or availability limited

active aeolian processes on mars a regional study in arabia and meridiani terrae 1 we present evidence of widespread aeolian activity in the arabia terra meridiani region mars where different kinds of aeolian modifications have been detected and classified passing from the regional to the local scale we describe one particular dune field in meridiani planum where two ripple populations are distinguished by means of different migration rates moreover a consistent change in the ripple pattern is accompanied by significant dune advancement between 0 4 1 meter in one martian year that is locally triggered by large avalanche features this suggests that dune advancement may be common throughout the martian tropics

on the origin and age of the great sand dunes colorado abstract over the past 100 yr several hypotheses have been proposed for the origin and age of the great sand dunes these hypotheses differ widely in the descriptions of dune morphometry the immediate source of eolian sand and when sand transport occurred the primary purpose of this paper is to evaluate these hypotheses and where warranted to present new ideas about the origin and age of the great sand dunes to evaluate the previous hypotheses we had to develop more detailed information about the surficial geology of the northern san luis valley thus we mapped the surficial geology of an area extending several tens of kilometers north south and west of the great sand dunes and examined subsurface stratigraphy in more than 200 wells and borings in addition we used relative dating criteria and several radiocarbon and osl ages to establish the chronology of surficial deposits and we determined the u pb ages of detrital zircons to obtain information about the sources of the sand in the great sand dunes the first principal finding of this study is that the lower part of the closed basin north of the rio grande referred to here as the sump is the immediate source of the sand in the great sand dunes rather than the late pleistocene flood plain of the rio grande the most widely accepted hypothesis a second principal finding is that the great sand dunes are older than late pleistocene they postdate the draining of lake alamosa which began 440 ka and predate the time when streams draining the west flank of the sangre de cristo mountains were deflected by incipient dunes that formed near the mountain front geomorphic and stratigraphic evidence indicate that this deflection occurred prior to the end of the next to last glaciation bull lake i e prior to 130 ka

magnetometer array studies earth structure and tectonic processes this review presents results from magnetovariation fields recorded by two dimensional arrays of magnetometers the emphasis is on the conductive structures mapped and studied and their tectonic implications eleven arrays were operated in north america between 1967 and 1985 a region of highly conductive uppermost mantle and or lower crust extending at least from 33 n to 54 n has been shown to extend beneath much of the continent west of the rocky mountains two recent investigations are discussed in more detail those of conductive structures under the canadian rockies and emslab electromagnetic sounding of the lithosphere and beyond array results for washington and oregon including a conductive strip beneath the cascades volcanoes correlations with high heat flow and seismic parameters make it reasonable to attribute these regional conductors to partial melting and or hot saline water within the craton the north american central plains conductor is discussed this narrow crustal feature is associated with a major fracture zone and age boundary which may be a plate boundary of proterozoic time an array beneath the auroral electrojet for study of the external currents is noted results from four array studies in southern africa are considered two of these relate to the southern cape conductive belt which correlates not with high heat flow but with a large static magnetic anomaly the magnetovariation magnetic and gravity anomalies and geological data can be accounted for if an accumulation of ophiolitic rocks including serpentine is present in the lower crust such an accumulation may have formed at a subduction in proterozoic time two other arrays delineated a conductive belt associated with the southwestern end of the african rift system in namibia subsequent resistivity soundings located a conductor of resistivity 10 ohm m at less than 4 km depth two array studies in india follow one in the north and one in the south the array in the himalayan foothills and indo gangetic plain mapped a conductor transverse to the regional strike this may be a fracture zone produced in the interplate collision with a rise of asthenospheric material such as fluids into the fractures the southern indian array reveals crustal conductors under the indo sri lankan graben and another under the comorin ridge southwest of the tip of the subcontinent array studies in central and southeastern australia and in fennoscandia in regions without large local conductivity anomalies have been used to study conductivity variation with depth a note on the carpathian crustal anomaly is included as an example of combination of response parameters secured at different times to form a virtual array

induction anomalies in geomagnetic sq in peninsular india anomalies in geomagnetic sq h sq z and sq d as recorded at an array of 21 magnetometers and 5 permanent observatories in peninsular india during 1979 1980 are analyzed and discussed in relation to geology signatures of the kodaikanal batholith the dharwar series of rocks and a graben structure in the palk strait on the geomagnetic records of nearby stations are unmistakably identified and associated with internal induction effect the extent and influence of the ionospheric equatorial electrojet and oceanic induced currents observed on the ground in this complex region are also mapped

asphalt volcanism and chemosynthetic life in the campeche knolls gulf of mexico in the campeche knolls in the southern gulf of mexico lava like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt which chilled and contracted after discharge the site also includes oil seeps gas hydrate deposits locally anoxic sediments and slabs of authigenic carbonate asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the gulf of mexico

biogeochemical controls on authigenic carbonate formation at the chapopote asphalt volcano bay of campeche abstract the campeche knolls in the bay of campeche southern gulf of mexico were investigated through detailed seafloor mapping rov surveys and sediment and pore water sampling the knolls are elongated submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor several of the knolls are associated with sea surface oil slicks identified from satellite data indicating the presence of hydrocarbon seeps on the seafloor one of the knolls named chapopote was studied in detail during two international research expeditions so174 2 and m67 2 and is characterized by extensive hydrocarbon seepage including large asphalt flows oil and gas seeps and seafloor gas hydrate deposits chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward diffusing seawater and hydrocarbon rich pore fluids at shallow sediment depth authigenic carbonates are characterized by aragonite exhibit a porous texture and are cemented by a matrix of microsparitic to sparitic aragonite macropores of the carbonates were completely filled with liquid oil carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism banded botryoidal aragonite cements line the intra and bioclasts and incompletely fill the pore spaces the stable carbon isotopic composition of authigenic aragonite varies between 28 6 and 17 9 pdb identifying oil oxidation as the primary source of carbon to the dic pool while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane aom these observations indicate the presence of additional aom independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the gulf of mexico basin oxygen isotope data of authigenic aragonite vary from 2 5 to 3 8 pdb indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids

evaluation of indian coastal response an integrated approach abstract since its separation 130 ma from the mainland the indian subcontinent has experienced major evolutionary changes a comparison of the structure evolution and tectonic elements of the east and west coast reveals characteristic differences thus while the eastern coast shows significant anomalous behaviour in all geophysical observations in contrast the corresponding observations on the western coast are relatively devoid of such anomalies in this investigation available magsat gravity electromagnetic gds and heatflow data have been utilized to search for a possible coherent cause for these different anomalies and thereby some inferences are sought to relate these causes to the geodynamics of this part of the indian plate

the mars regional atmospheric modeling system model description and selected simulations the mars regional atmospheric modeling system mrams is introduced and selected model results are presented and compared with landed meteorological data when possible mrams is descended from a nonhydrostatic earth mesoscale and cloud scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain mesoscale models such as mrams are ideal tools for making use of the high resolution data sets arriving from mars global surveyor experiments simulation of the mars pathfinder mpf landing site at lsd 142 using 1 2 degree mars orbiter laser altimeter mola derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near surface temperature pressure and wind direction simulations of topographically induced thermal circulations and mountain induced gravity waves are shown to be consistent with theory and earlier studies that tie large amplitude mountain waves to strong winds capable of producing dust streaks and local dust lifting events a large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux momentum flux turbulent kinetic energy and vertical velocity variance the model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon but fluxes are roughly an order of magnitude smaller due to the lower density dust devillike circulations are also predicted in the large eddy simulation finally a simulation that examines atmosphere surface interactions near big crater is discussed predicted surface wind stress patterns are consistent with aeolian processes inferred through mars orbiter camera imagery of big crater located near the mpf landing site c 2001 academic press

controls of eolian dune size and spacing data for the namib and gran desierto sand seas suggest that the controls of dune size and spacing are complex the relation between dune height and spacing varies with dune type and location and reflects both dune dynamics vertical accretion vs migration or extension and availability of sand there is no general relation between dune spacing and grain size in the namib sand sea the height of compound and complex dunes draas is inversely proportional to potential sand transport rates whereas the height of dunes superimposed on their flanks varies directly with potential sand transport rates these observations can be combined with data on dune spacing to demonstrate the existence of a hierarchy of eolian dunes each element of which responds to variations in sand transport rates at different temporal and spatial scales whereas the morphology of individual simple dunes and superimposed dunes on draas is related to contemporary rates and directions of sand transport the morphology and development of draas reflects long term and regional patterns of sand transport and deposition

interpretation of the complex dune morphology on mars dune activity modelling and a terrestrial analogue in this work we analyze a dark erg on mars that could be considered a mega dune draa where secondary dunes of different morphology are superposed over a main crescent shaped bedform primary dune the presence of a complex multi directional wind regime is indicated as one of the main causes for the accumulation of a tall draa presenting an analogy to the great sand dunes in colorado in both cases main regional winds from the sw blow in opposition to winds from the ne which are enhanced by the topography such a complex wind regime leads to the development of star and reversing dunes and is accurately predicted by atmospheric models on a regional and local scale signs of activity in the form of grainflow scars are also noted over the slip faces of many dunes suggesting that easterly winds are actively shaping the study draa in the present day climatic setting the presence of this draa on mars suggests a complex interaction between regional and local topographically controlled flows and a consistent availability of sand the future study of an analogue terrestrial site such as the great sand dunes could be fundamental for understanding the evolution of similar martian dune fields copyright 2012 john wiley sons ltd

southern high latitude dune fields on mars morphology aeolian inactivity and climate change in a study area spanning the martian surface poleward of 50 s 1190 dune fields have been identified mapped and categorized based on dune field morphology dune fields in the study area span 116 400 km2 leading to a global dune field coverage estimate of 904 000 km2 far less than that found on earth based on distinct morphological features the dune fields were grouped into six different classes that vary in interpreted aeolian activity level from potentially active to relatively inactive and eroding the six dune field classes occur in specific latitude zones with a sequence of reduced activity and degradation progressing poleward in particular the first signs of stabilization appear at 60 s which broadly corresponds to the edge of high concentrations of water equivalent hydrogen content observed by the neutron spectrometer that have been interpreted as ground ice this near surface ground ice likely acts to reduce sand availability in the present climate state on mars stabilizing high latitude dunes and allowing erosional processes to change their morphology as a result climatic changes in the content of near surface ground ice are likely to influence the level of dune activity spatial variation of dune field classes with longitude is significant suggesting that local conditions play a major role in determining dune field activity level dune fields on the south polar layered terrain for example appear either potentially active or inactive indicating that at least two generations of dune building have occurred on this surface many dune fields show signs of degradation mixed with crisp brinked dunes also suggesting that more than one generation of dune building has occurred since they originally formed dune fields superposed on early and late amazonian surfaces provide potential upper age limits of 100 my on the south polar layered deposits and 3 ga elsewhere at high latitudes no craters are present on any identifiable dune fields which can provide a lower age limit through crater counting assuming all relatively stabilized dune fields represent a single noncontiguous surface of uniform age their estimated crater retention age is 10 000 years an average sized uncratered dune field 94 km2 has a crater retention age 8 my this apparent youth suggests that present day climate conditions are responsible for the observed degradation and reduced level of aeolian activity a lack of observed transport pathways and the absence of large dune fields in the largest basins hellas and argyre planitiae are consistent with the previously proposed idea that dune sands are not typically transported far from their source regions on mars

microstructures of structure i and ii gas hydrates from the gulf of mexico gas hydrate samples from various locations in the gulf of mexico gom differ considerably in their microstructure distinct microstructure characteristics coincide with discrete crystallographic structures gas compositions and calculated thermodynamic stabilities the crystallographic structures were established by x ray diffraction using both conventional x ray sources and high energy synchrotron radiation the microstructures were examined by cryo stage field emission scanning electron microscopy fe sem good sample preservation was warranted by the low ice fractions shown from quantitative phase analyses gas hydrate structure ii samples from the green canyon in the northern gom had methane concentrations of 70 80 and up to 30 of c2 c5 of measured hydrocarbons hydrocarbons in the crystallographic structure i hydrate from the chapopote asphalt volcano in the southern gom was comprised of more than 98 methane fairly different microstructures were identified for those different hydrates pores measuring 200 400 nm in diameter were present in structure i gas hydrate samples no such pores but dense crystal surfaces instead were discovered in structure ii gas hydrate the stability of the hydrate samples is discussed regarding gas composition crystallographic structure and microstructure electron microscopic observations showed evidence of gas hydrate and liquid oil co occurrence on a micrometer scale that demonstrates that oil has direct contact to gas hydrates when it diffuses through a hydrate matrix

seismic characterization of hydrates in faulted fine grained sediments of krishna godavari basin unified imaging 1 a combination of diffusion and advection in fine grained sediments can create a patchy bottom simulating reflector bsr which has little to no apparent correlation with the overlying hydrate distribution using 2d seismic data from faulted clay rich sediments in the krishna godavari kg basin we show both the hydrate distribution and the bsr structure are fault controlled our demonstration hinges upon a kinematically accurate p wave velocity vp model which is estimated using a composite traveltime inversion depth migration method in an iterative manner the flexibility of the method allows simultaneous usage of traveltimes from multiple discontinuous reflectors the application begins with a simple vp model from time processing which is reflective of a diffusive continuous hydrate and free gas bearing system the application converges in three iterations yielding a final vpmodel which is suggestive of a patchy distribution of hydrates and free gas possibly developing through a combined diffusive advective system the depth image corresponding to the final vp model can be interpreted for faults that suggest ongoing tectonism the bsr appears to be truncated at active faults zones both the final vp model and the corresponding depth image can be reconciled with the hydrate distribution and bsr depth at logging coring sites located 250 m away from the line by projecting the sites along the strike direction of the regional faults

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

geomagnetic coast and other effects deduced from the new observatory at visakhapatnam india summary coastal effects observed in the long period sq solar quist day ranges and short period changes over 30 min intervals during magnetic substorms bays as recorded at a new magnetic observatory at visakhapatnam on the east coast of india during 1995 in the h z and d elements are analysed and the preliminary results are discussed the results are compared with those from alibag and hyderabad located more or less at the same latitude based on simultaneous 1995 records short period induction vectors are computed and the arrows presented and discussed at the three locations while the enhancement associated with close proximity to the coast in sq z at alibag on the west coast compared to the central inland station of hyderabad enhancement of 17 37 per cent is quite prominent in all three seasons of the year at visakhapatnam it is only marginally observed during the d season at bay frequencies medium sized induction arrows point towards the nearest deep sea conductive body at both alibag and visakhapatnam while it is towards the southeast with a considerably reduced magnitude at hyderabad these induction arrows and the effects on sq z sq h and sq d ranges are discussed in conjunction with the parkinson arrows and sq z sq h and sq d ranges from margao west coast dharwar bellary mahanandi chirala east coast at the latitude of the 16 n profile of an earlier array experiment and the two are interpreted together

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

aeolian dune field self organization implications for the formation of simple versus complex dune field patterns abstract the interpretation of aeolian dune field patterns as self organizing complex systems is a new paradigm in which pattern evolution may be addressed computer simulations supported by field and experimental data indicate that a given wind regime produces a simple dune field pattern dune type and crest orientation are determined by wind regime and pattern ordering occurs through dune dune interactions over time because dunes reorient only at their crest terminations with a change in wind regime the rate of formation of a new pattern of small dunes is typically faster than the rate of reorientation of the existing pattern resulting in the superposition of simple patterns to give rise to complex patterns complex patterns are distinct from spatial changes in a simple pattern and from the type of superposition that characterizes compound complex dunes complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface

a magnetometer array study in northwest india abstract a magnetometer array study has been carried out in northwest india from rajasthan across the indo gangetic plain into the himalayan foothills over the three months of operation a wide variety of natural geomagnetic events has been recorded the analysis of a simple substorm polarized just west of north shows a strong anomaly in the form of a reversal of the vertical component of the fluctuation both in the himalayan foothills and on the ganga plain the magnetic fluctuations pattern observed is most directly interpreted in terms of a path of concentrated current flow in the earth striking across the himalaya it is evidently aligned with the aravalli belt which outcrops further south and may indicate that some geological structure in the sub basement is of abnormally high electrical conductivity the path of such a current concentration across the foothills raises the question whether some transverse structure in the himalaya is not acting as a bridge to peninsular india for current induced in the tibetan plateau to the northeast

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

seismic stratigraphy of veracruz tongue deep southwestern gulf of mexico the veracruz tongue is a region of continental slope and rise sediments bounded bathymetrically by the mexican ridges fold belt to the west and the campeche knolls salt province to the east study of two multichannel seismic lines and single fold sparker data enables five post early miocene seismic stratigraphic sequences to be distinguished in the tongue sedimentary processes responsible for deposition of each sequence are inferred on the basis of external geometry internal reflection configuration and where possible core data the five sequences are each interpreted to consist of turbidites grading laterally into hemipelagites these primary deposits may be modified later by downslope creep or sliding and slumping because bathymetry is a major control on location of turbidity current flows slides and slumps the depositional history of the veracruz tongue provides indirect evidence of tectonic evolution of the mexican ridges fold belt and the campeche knolls salt province salt domes first formed a barrier to turbidity current flow from the east at the close of the middle miocene the mexican ridges fold belt evolved gradually until it formed a complete barrier to turbidity current flow from the west at the close of the pliocene as a result of shift in direction of turbidity current flow through time potentially sand prone miocene turbidites are overlain by hemipelagic clays and clayey oozes a situation favorable to hydrocarbon entrapment

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

investigation of the age and migration of reversing dunes in antarctica using gpr and osl with implications for gpr on mars gpr provides high resolution images of aeolian strata in frozen sand in the mcmurdo dry valleys of antarctica the results have positive implications for potential gpr surveys of aeolian strata on mars within the lower victoria valley seasonal changes in climate and a topographically constrained wind regime result in significant wind reversals as a consequence dunes show reversing crest lines and flattened dune crests ground penetrating radar gpr surveys of the dunes reveal sets of cross strata and low angle bounding surfaces produced by reversing winds summer sand transport appears to be dominant and this is attributed to the seasonal increase in solar radiation solar radiation which heats the valley floor melts ice cements making sand available for transport at the same time solar heating of the valley floor generates easterly winds that transport the sand contributing to the resultant westward dune migration the location of the dune field along the northern edge of the lower victoria valley provides some shelter from the powerful foehn and katabatic winds that sweep down the valley topographic steering of the winds along the valley and drag against the valley wall has probably aided the formation migration and preservation of the dune field optically stimulated luminescence osl ages from dune deposits range from 0 to 1 3 kyr showing that the dune field has been present for at least 1000 yr the osl ages are used to calculate end point migration rates of 0 05 to 1 3 m yr which are lower than migration rates reported from recent surveys of the packard dunes and lower than similar sized dunes in low latitude deserts the relatively low rates of migration are attributed to a combination of dune crest reversal under a bimodal wind regime and ice cement that reduces dune deflation and restricts sand entrainment

inverse maximum gross bedform normal transport 1 how to determine a dune constructing wind regime using only imagery abstract it has been a goal of aeolian science to use bedforms as indicators of local and regional sediment transport and atmospheric circulation but even with the application of the rule of maximum gross bedform normal transport mgbnt the underdetermined nature of the problem has precluded its application in all but the most simple cases we present a method to apply the rule of mgbnt and its inverse imgbnt from analysis of aeolian dune crestlines derived from aerial imagery although the solutions to imgbnt analysis are non unique the possible transport vectors influencing bedform morphology can often be constrained by making inferences regarding bedform type e g transverse oblique or longitudinal resultant drift direction and the ratio of transport vector magnitudes the technique is demonstrated on the great sand dunes located in colorado usa this dune field has a wide array of dune morphologies eight crestline sets were identified and mapped imgbnt analysis and the subsequent constraint of possible solutions suggests that transport vectors from the southeast and southwest with a se sw transport ratio of 1 2 produce oblique north south oriented dunes that dominate the main dune field these results compare favorably with mgbnt analysis of meteorologic measurements from three stations located adjacent to the great sand dunes which predict dune types and orientations similar to those observed in their vicinity

geotectonic remobilisation of the lower crustal segment of southern peninsular india abstract deep crustal exposures on various continental platforms have recently attracted much attention with regard to their evolution and relevance to present day tectonics the granulite terrain of the southern part of peninsular india exhibits unique characteristics the small dimensions bounded by two rifted margins high relief as a result of recent uplift and anomalous gravity magnetic and electromagnetic signatures the geophysical anomalies over this region have been cohered to produce a tentative geodynamic model in which the break up of gondwana 150 my bp subsequent rifting of the western margin of india 70 my bp and the collision with asia and post collision stresses 50 my bp play a role in the remobilisation of the crust mantle regime of south india the geophysical signatures over this deep crustal cross section differ markedly from those of its counterparts in other parts of the world and thus may reflect the consequences of recent remobilisation rather than features frozen in since proterozoic time in this sense deep crustal imaging of southern peninsular india may differ from that in other continental platforms

the martian dust storm of sol 1742 after nearly five earth years on mars the mutch memorial station viking lander 1 finally witnessed a local dust storm that eroded trenches conical piles and other disturbed surfaces in the sample field and near the lander the event called the dust storm of sol 1742 occurred late in the third winter of lander observations between sols 1728 and 1757 analyses of tiny new wind tails and movement of materials indicate that the eroding winds were variable but more northeasterly than those that had previously shaped the surface pebbly residues and movement of 4 5 mm clods suggest drag velocities or friction speeds of the winds were about 2 2 4 0 m s wind speeds at the height of the meteorology boom 1 6 m were probably about 40 50 m s much of the observed erosion could have occurred in a few to several tens of seconds but somewhat longer times are suggested by analogy with the erosion of terrestrial soils most of the erosion occurred where preexisting equilibrium conditions of surface configurations and surface material properties had been altered by the lander during landing and during surface sampler activities but thin layers of bright fine grained dust were also removed and redistributed surfaces where preexisting equilibrium conditions were unaltered appeared to be uneroded

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

regional electromagnetic induction around the indian peninsula and sri lanka a three dimensional numerical model study using the thin sheet approximation abstract further to other recent numerical studies of geomagnetic induction in southern india the thin sheet algorithm developed at the university of victoria has been used to investigate the three dimensional problem of induction by a uniform source over the indian peninsula and sri lanka with this algorithm it is not necessary to assume that the region is surrounded by a normal structure but the limitations imposed by grid size and the given conductivities for the crust and mantle have restricted our study to an inducing field of 20 min period solutions have been computed for two different models 1 with only the conductivity contrast arising from land and seawater of variable depth present and 2 with additional sub surface conductors included in the palk strait gulf of manowar region underneath or near the comorin ridge and along the west coast fault results are presented for uniform magnetic sources oriented in both the northward and westward directions to distinguish the effect of different polarizations the correspondence between the observed and computed parkinson arrows at the southern array stations suggests the existence of the three sub surface conductors

a scaling law for aeolian dunes on mars venus earth and for subaqueous ripples abstract the linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength at which the bed destabilises to form dunes should scale with the drag length l drag s f d this scaling law is tested using existing and new measurements performed in water subaqueous ripples in air aeolian dunes and fresh snow dunes in a high pressure co2 wind tunnel reproducing conditions close to venus atmosphere and in the low pressure co2 martian atmosphere martian dunes the difficulty is to determine the diameter of saltating grains on mars a first estimate comes from photographs of aeolian ripples taken by the rovers opportunity and spirit showing grains whose diameters are smaller than on earth dunes in addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds it confirms that the small grains visualised by the rovers should be grains experiencing saltation finally we show that within error bars the scaling of with ldrag holds over almost five decades we conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on mars

three mars years viking lander 1 imaging observations the mutch memorial station viking lander 1 on mars acquired imaging and meteorological data over a period of 2245 martian days 3 3 martian years this article discusses the deposition and erosion of thin deposits ten to hundreds of micrometers of bright red dust associated with global dust storms and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities except for redistribution of thin layers of materials the surface appears to be remarkably stable perhaps because of cohesion of the undisturbed surface material

aeolian processes in proctor crater on mars sedimentary history as analyzed from multiple data sets 1 proctor crater is a 150 km diameter crater in noachis terra within the southern highlands of mars the analysis leading to the sedimentary history incorporates several data sets including imagery elevation composition and thermal inertia mostly from the mars global surveyor mission the resulting stratigraphy reveals that the sedimentary history of proctor crater has involved a complex interaction of accumulating and eroding sedimentation aeolian features spanning much of the history of the crater interior dominate its surface including large erosional pits stratified beds of aeolian sediment sand dunes erosional and depositional streaks dust devil tracks and small bright bed forms that are probably granule ripples long ago up to 450 m of layered sediment filled the crater basin now exposed in eroded pits on the crater floor these sediments are probably part of an ancient deposit of aeolian volcaniclastic material since then some quantity of this material has been eroded from the top layers of the strata small bright dune forms lie stratigraphically beneath the large dark dune field relative to the large dark dunes the bright bed forms are immobile although in places their orientations are clearly influenced by the presence of the larger dunes their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill dust devil tracks form during the spring and summer following a west southwesterly wind early in the spring the dust devils are largely restricted to dark patches of sand as the summer approaches dust devil tracks become more plentiful and spread to the rest of the crater floor indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils the dark dunes contain few dust devil tracks suggesting that accumulated dust is swept away directly by saltation rather than by the passage of dust devils spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt like materials the average thermal inertia calculated from thermal emission spectrometer bolometric temperatures is 277 17 j m 2 s 0 5 k 1 leading to an effective grain size of 740 170 mm which is consistent with coarse sand and within the range expected for martian sand the coarse sand that composes the large dune field may have originated from outside the crater saltating in from the southwest most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried the sand was transported to the east center of the crater floor where beneath the present day dunes a 50 m high mound of sand has accumulated dune slip faces indicate a wind regime consisting of three opposing winds some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms the combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime which produces the large reversing transverse and star dunes that dominate the dune field the dark dunes have both active slip faces and seemingly inactive slip faces suggesting that the dunes vary spatially in their relative activity nevertheless the aeolian activity that has dominated the history of proctor crater still continues today index terms 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5410 planetology solid surface planets

pervasive aeolian activity along rover curiosity s traverse in gale crater mars the nasa mars science laboratory msl rover curiosity has safely landed near a 35 km long dark dune field in gale crater on mars this dune field crosses the landing site from the northeast to the southwest and lies along curiosity s traverse to aeolis mons here we present the first evidence of recent aeolian activity in the form of ripple and dune migration and further estimate wind directions within the dune field through analysis of ripple and dune morphologies and the mars regional atmospheric modeling system mrams we measured a minimum ripple migration rate of 0 66 m per earth year and dune migration rate of 0 4 m per earth year in the southwest portion of the field a strongly bidirectional ripple crestline orientation nearly orthogonal dune slipfaces and linear seif or oblique dunes indicate a bidirectional wind regime with winds mainly coming from the ene and from the northwest however mrams results indicate primary winds from the ene our constraints on the wind regime provide the unique opportunity to use ground measurements from msl to test the accuracy of winds predicted from orbital data