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

ventifacts at the pathfinder landing site about half of the rocks at the mars pathfinder ares vallis landing site appear to be ventifacts rocks abraded by windborne particles comparable resolution images taken by the imager for mars pathfinder imp camera and the viking landers show that ventifacts are more abundant at the pathfinder site the ventifacts occur in several forms including rocks with faceted edges finger like projections elongated pits flutes grooves and possible rills the trends of elongated pits flutes grooves and rills cluster at 280 330 clockwise from north and generally dip 10 30 away from their trend direction these orientations are indicative of southeast to northwest winds and differ from the trend of wind tails at the landing site the direction of local wind streaks and predictions of the global circulation model all of which indicate northeast to southwest winds the disparity between these data sets strongly suggests that local circulation patterns have changed since the abrasion of the ventifacted rocks the greater number of ventifacts at the pathfinder site compared to either of the viking sites is most easily explained as being due to a larger supply of abrading particles composed of either sand sized grains or indurated dust aggregates and higher surface roughness which should increase the momentum of saltating grains the pathfinder ventifacts may have formed shortly after the deposition of outflow channel sediments nearly 2 gry ago when a large local supply of abrading particles should have been abundant and atmospheric conditions may have been more conducive to rock abrasion from saltating grains based on how ventifacts form on earth the several ventifact forms seen at the pathfinder site and their presence on some rocks but not on others are probably due to local airflow conditions original rock shape exposure duration rock movement and to a lesser extent rock lithology the abundance of ventifacts at the pathfinder site together with other evidence of weathering indicates that unaltered rock surfaces are rare on mars

distribution of rocks on the gusev plains and on husband hill mars 1 the population of rocks larger than 15 cm in diameter was measured at 36 locations imaged by the spirit rover over 4 km of the traverse across the gusev plains and husband hill in gusev crater on mars the rock population observed on plains surfaces is consistent with impact fragmentation of rubbly fractured volcanics and reveals little evidence for modification by secondary processes or weathering interpretation of counts from husband hill suggest an influence by bedrock for rocks larger than 0 5 m across but the distribution of smaller rocks is consistent with ejecta possessing contributions from pre plains impact events results indicate plains surfaces experienced only tens of centimeters of eolian erosion deposition since the hesperian whereas meters rather than tens of meters of erosion modified husband hill since the early hesperian

partial self reversal of trm in baked soils and ceramics from ecuador abstract partial self reversed thermoremanent magnetizations srtrms were observed in samples of baked soils hearths and ceramics from the rumipamba archeological site near quito ecuador and ceramics from sites near the town of esmeraldas ecuador the srtrms were recognized at room temperature on few samples but cooling the samples in liquid nitrogen enhanced the intensity of the srtrm and measurement at 77 k enables its rapid detection in many samples from these sites alternating field demagnetization of the srtrm indicate median destructive field of the order of 50 mt and thermal demagnetization give unblocking temperatures in the temperature range 280 380 c the magnetic carriers of the srtrm are stable to heating in air or in vacuum up to 600 c suggesting that titanomaghemite should not be the magnetic carrier of the srtrm the studied baked clays and ceramics contain detrital material of mainly volcanic origin ti poor titanomagnetite is the main magnetic carrier identified by strong field data or susceptibility measurements versus temperature ilmeno hematite grains were recognized with microscope observations under reflected light scanning electron microscope observations with energy dispersive x ray spectrometry indicate a ti fe ratio corresponding to an ilmenite content of 0 55 we also compared the magnetic properties of the partially self reversed baked clays with those of the self reversed pinatubo pumices the srtrms were measured upon cooling from room temperature to 20 k with the mpms upon cooling to 20 k the srtrm show a nearly tenfold increase in intensity with respect to the room temperature measurement the baked clay and ceramics from ecuador carrying the srtrm share similar magnetic properties with the pinatubo pumices unblocking temperatures low temperature behavior supporting the interpretation that detrital hemoilmenite originating from the holocene activity of the numerous ecuadorian volcanoes is the main carrier of the srtrm in the archeological samples in some samples anisotropy tensors of srtrm show large anisotropy degree 2 the high anisotropy observed when the total magnetization is the sum of a normal thermoremanent magnetization trm and a srtrm is likely amplified because the anisotropy carried by the srtrm is larger than the one carried by the normal component a component of srtrm may be hidden in archeological materials containing detrital hemoilmenites related to dacitic andesitic volcanism and this may affect the determination of paleointensity of the earth magnetic field especially when non thermal method are used

domain observations of the magnetic phases in volcanics with self reversed magnetization the temperature dependence of magnetic domain pattern in titanomagnetite and titanohematite of self reversing andesites from the 1985 eruption of the nevado del ruiz volcano colombia has been observed using the bitter technique during heating cooling cycles in the laboratory the natural remanent magnetization loses the self reversal properties between 110 c and 180 c the titanohematite domains disappear in the same temperature interval large grain regions without visible colloid contrast are observed between room temperature and 180 c utilizing the high resolution of a magnetic force microscope it is found that these regions contain either domains with wall spacing of about 3 m or a buckling pattern along the phase boundary between a titanomagnetite and a titanohematite grain but within the titanohematite a 2 m wide chemically different domain has been observed it has a higher iron content than the main titanohematite the two titanohematite phases represent two phases with higher curie temperature tc but lower spontaneous magnetization ms and lower tc but higher ms respectively negative interaction between these phases is called upon to explain the self reversing mechanism

latitude dependent nature and physical characteristics of transverse aeolian ridges on mars 1 narrow angle images from the mars orbiter camera moc have revealed the common occurrence of small scale 100 m wavelength bright transverse aeolian ridges tars on the surface of mars moc images were used to assess the broad distribution of tars from 90 n to 90 s between 180 e and 240 e to investigate their relationship to latitude elevation thermal inertia geologic units local slopes and surface roughness out of 5112 examined images from the primary mission 520 10 contain evidence of tars 92 of the images with tars are located between 50 latitude and very few occur in the middle to upper latitudes or polar regions of either hemisphere tars are observed at elevations from 5 km to 3 km with the highest frequency 26 between 1 and 0 km there is no systematic relationship between the distribution of tars and global thermal inertia measurements most tars occur in geologic units associated with the channel system materials 39 and the olympus mons aureole 33 at a length scale of 1 85 km pixel the average local slopes for images with and without tars are 1 92 and 1 36 respectively of the parameters investigated the latitudinal trend of tars in both hemispheres appears to be predominantly related to surface roughness with a positive linear correlation between the surface roughness of geologic units and frequency of tars r2 0 87 factors affecting the semiglobal distribution of tars are likely related to the climate and wind regimes in which they formed but do not provide definitive evidence for either saltation or reptation formation mechanisms

a detailed magnetic and mineralogical study of self reversed dacitic pumices from the 1991 pinatubo eruption philippines 39 dacitic pumice and lithic samples from the 1991 eruption of mount pinatubo were investigated through both magnetic and mineralogical means as in a previous study natural remanent magnetization nrm is found to be reversed for most of the samples with respect to the direction of the actual geomagnetic field direction a few samples amongst them ancient lithics transported by pyroclastic flows show scattered nrm directions from thermal demagnetization of these particular samples it is concluded that their orientation changed after emplacement the emplacement temperature is estimated to be more than 460 c from thermal demagnetization of lithic samples two magnetic minerals with large grain sizes are observed under the optical microscope titanomagnetite tm and haemo ilmenite hem ilm microprobe analyses yield x 0 10 for tm and y 0 52 and y 0 54 for two hem ilm phases in agreement with the observed curie temperatures 480 c for tm and 250 c for hem ilm the hem ilm particles display chemical zonation which seems to be correlated with a change of the domain structure typically a ferrimagnetic fm phase with slightly higher titanium content is observed in the central part whilst the crystal margin which is weakly ferromagnetic wf due to spin canted antiferromagnetism is slightly poorer in titanium two different mechanisms for the origin and formation of the two observed phases are discussed 1 chemical zonation of hem ilm crystals due to a change in conditions in the magma chamber shortly before eruption 2 similar to the microstructures observed from synthetic samples this zonation in the large natural hem ilm could be the result of migration of the wf phase towards the grain boundary during residence below the order disorder transition temperature in the magmatic chamber the room temperature hysteresis loop which seems to be dominated by tm provides multidomain md like parameters jrs js 0 01 and hcr hc 20 the large coercivity of remanence 15 40 mt which is attributed to hem ilm may be intrinsic or due to interactions between wf and fm phases the field dependence of the magnitude of the thermoremanent magnetization trm is not linear it increases first reaches a maximum negative value for an applied field h close to 0 5 mt then decreases steadily by extrapolation it is estimated that the trm should be zero for a field of about 12 mt and become positive beyond this total trm is in fact the sum of several components af demagnetization of trms acquired in different fields shows the presence of at least three components a self reversed sr component that contains both hard and moderately hard components and a soft normal component independently of the value of h the median destructive field of the sr component is of the order of 70 mt which suggests that the fm phase is not entirely locked by exchange interaction with the wf phase and can experience noticeable wall movements however some 20 per cent of the sr trm component remains after af treatment of 220 mt although we believe that exchange interaction plays a key role in the process of sr trm acquisition torque curves in the high field of samples both with and without sr trm do not show clear evidence for unidirectional anisotropy similarly we do not observe any significant shift of major hysteresis loops or non vanishing hysteresis losses two characteristics generally considered as indicative of exchange anisotropy and usually observed for synthetic single domain pseudo single domain sd psd hem ilm indeed in addition to the exchange interaction the magnetostatic coupling must play some role here because of the large size of the hem ilm grains

self reversal of natural remanent magnetization in andesitic pumice abstract the natural remanent magnetization of andesitic pumice erupted from the nevado del ruiz volcano colombia in 1985 is reversed with respect to the present geomagnetic field because of self reversal laboratory thermoremanent magnetization acquired in fields of

mars pathfinder landing site evidence for a change in wind regime from lander and orbiter data surface features related to the wind are observed in the vicinity of the mars pathfinder mpf landing site data from the lander and in data from orbit by the viking orbiter and mars global surveyor missions features seen from the surface include wind tails associated with small rocks barchanoid duneforms ripplelike patterns and ventifact flutes cut into some rocks features seen from orbit include wind tails associated with impact craters ridges inferred to be duneforms and modified crater rims interpreted to have been eroded and mantled by windblown material the orientations of these features show two prevailing directions one is inferred to represent winds from the northeast which is consistent with strongest winds predicted by a general circulation model to occur during the martian northern winter under current conditions a second wind blowing from the ese was responsible for modifying the crater rims and cutting some of the ventifacts the two wind regimes could reflect a change in climate related to mars obliquity or some other unknown factor regardless of the cause the mpf area has been subjected to a complex pattern of winds and supply of small particles and the original surface formed by sedimentary processes from tiu and ares vallis flooding events has been modified by repeated burial and exhumation

gusev crater wind related features and processes observed by the mars exploration rover spirit 1 wind related features observed by the rover spirit in gusev crater mars include patches of soil on the surface some of which are organized into bed forms windblown grains include dust inferred to be 2 mm in diameter microscopic imager data show the sands and granules to be rounded and relatively spherical typical of grains transported long distances by the wind the interior of bed forms exposed by rover operations suggests the infiltration of dust among the grains indicating that these sands are not currently experiencing saltation orientations of 1520 features such as bed forms and ventifacts along spirit s traverse from the landing site the columbia memorial station to west spur in the columbia hills suggest primary formative winds from the north northwest which correlate with measurements of features seen in orbiter images and is consistent with afternoon winds predicted by atmospheric models a secondary wind from the southeast is also suggested which correlates with predictions for nighttime early morning winds wind abrasion is indicated by ventifacts in the form of facets and grooves cut into rocks the orientations of which also indicate prevailing winds from the north northwest orientations of many aeolian features in the west spur area however have more scatter than elsewhere along the traverse which is attributed to the influence of local topography on the patterns of wind active dust devils observed on the floor of gusev from the columbia hills demonstrate that dust is currently mobile sequential images of some dust devils show movement as rapid as 3 8 m s consistent with wind velocities predicted by atmospheric models for the afternoon when most of the dust devils were observed sands accumulated on the rover deck in the same period suggest that some sands in the columbia hills experience active saltation two toned rocks having a light band coating at their bases are considered to represent partial burial by soils and subsequent exposure while perched rocks could represent materials lowered onto other rocks by deflation of supporting soils measurements of the heights of the light bands and the perched rocks range from 1 cm to 27 cm indicating local deflation by as much as 27 cm

source rock characterization and petroleum systems of eocene tyee basin southern oregon coast range usa the hydrocarbon source rock potential of the eocene units in the southern oregon coast range was evaluated using rock eval pyrolysis most eocene units in southern oregon coast range are thermally immature and contain lean gas prone type iii kerogen however some beds coals are sufficiently organic rich to be sources of biogenic and thermogenic methane discovered in numerous seeps the overall hydrocarbon source rock potential of the southern oregon coast range is moderately low however requirements for commercial accumulations of hydrocarbon probably exist locally within and adjacent areas two speculative petroleum systems are proposed the first includes the southern part of the oregon coast range near the border with the mesozoic klamath mountains and is related to a proposed subduction zone maturation mechanism along thrust faults the second occurs near the eastern border of the range where maturation is related to heating by sills and migration of hydrothermal fluids associated with mid tertiary volcanism in the western cascade arc

reversed magnetization in pyroclastics from the 1985 eruption of nevado del ruiz colombia one of the fundamental principles of palaeomagnetism and rock magnetism states that the direction of natural remanent magnetization nrm is acquired parallel to the applied field however ferromagnetic mineral phases with complex microstructures may violate this rule1 2 and produce a magnetization vector which is antiparallel to the direction of the external field andesitic pumice which was hurled several kilometres during the disastrous 1985 eruption of the nevado del ruiz volcano colombia carries a stable but reversed nrm with southerly declination and negative inclination heating experiments show that this magnetization is due to a self reversal mechanism which also induces a reversed thermoremanent magnetization trm in the laboratory field thus we have used the nevado del ruiz 1985 pumice which was magnetized in the present well known geomagnetic field to demonstrate for the first time that self reversal has actually controlled the process of nrm acquisition

paleointensity of the earth s magnetic field during the laschamp excursion and its geomagnetic implications the reversed paleomagnetic direction of the laschamp and olby flows represents a specific feature of the geomagnetic field this is supported by paleomagnetic evidence showing that the same anomalous direction was recorded at several distinct sites including scoria of the laschamp volcano to examine this anomalous geomagnetic fluctuation we studied the paleointensity of the laschamp and olby flows using the thellier method twenty five samples were selected for the paleointensity experiments and from seven we obtained reliable results because the paleointensity results of the olby and laschamp flows as well as laschamp scoria are very similar they can be represented by a single mean paleointensity f 7 7 t considering that this low paleointensity is less than 1 6 of the present geomagnetic field and is more characteristic of transitional behavior our results suggest that the paleomagnetic directions of the laschamp and olby flows were not acquired during a stable reversed polarity interval a more likely explanation is that the laschamp excursion represents an unsuccessful or aborted reversal

columbia hills mars aeolian features seen from the ground and orbit 1 abundant wind related features occur along spirit s traverse into the columbia hills over the basaltic plains of gusev crater most of the windblown sands are probably derived from weathering of rocks within the crater and possibly from deposits associated with ma adim vallis windblown particles act as agents of abrasion forming ventifacts and are organized in places into various bed forms wind related features seen from orbit results from atmospheric models and considerations of topography suggest that the general wind patterns and transport pathways involve 1 winter nighttime winds that carry sediments from the mouth of ma adim vallis into the landing site area of spirit where they are mixed with locally derived sediments and 2 winter daytime winds that transport the sediments from the landing site southeast toward husband hill similar patterns occur in the summer but with weaker winds reversals of daytime flow out of gusev crater and nighttime wind flow into the crater can account for the symmetry of the bed forms and bimodal orientations of some ventifacts

importance of titanohematite in detrital remanent magnetizations of strata spanning the cretaceous paleogene boundary hell creek region montana intermediate composition titanohematite fe2 ytiyo3 with 0 5 y 0 7 is seldom the focus of paleomagnetic study and is commonly believed to be rare in nature while largely overlooked in magnetostratigraphic studies intermediate titanohematite has been identified as the dominant ferrimagnetic mineral in an array of late mesozoic and early cenozoic laramide clastic deposits throughout the central united states intermediate titanohematite is ferrimagnetic and has similar magnetic properties to titanomagnetite except its unique self reversing property due to these similarities and with detrital remanent magnetizations masking its self reversing nature intermediate titanohematite is often misidentified in sedimentary deposits past studies relied upon nonmagnetic techniques including x ray diffraction and electron microprobe analysis while these techniques can identify the presence of intermediate titanohematite they fail to test whether the mineral is the primary recorder to facilitate the identification of intermediate titanohematite in sedimentary deposits we characterize this mineral using low temperature magnetometry and high temperature susceptibility experiments and present a new identification technique based on titanohematite s self reversing property for sediments that span the cretaceous paleogene boundary hell creek region montana results from the self reversal test indicate that the majority of remanence is held by minerals that become magnetized parallel to an applied field but that intermediate self reversing titanohematite y 0 53 0 63 is an important ancillary carrier of remanence while earlier literature suggests that intermediate titanohematite is rare in nature reanalysis using specialized rock magnetic techniques may reveal that it is more abundant in the rock record particularly within depositional basins adjacent to calc alkaline volcanics than previously thought

physical properties of the mars exploration rover landing sites as inferred from mini tes derived thermal inertia 1 the miniature thermal emission spectrometer mini tes on board the two mars exploration rovers provides the first opportunity to observe thermal properties from the martian surface relate these properties to orbital data and perform soil conductivity experiments under martian conditions the thermal inertias of soils bedforms and rock at each landing site were derived to quantify the physical properties of these features and understand geologic processes occurring at these localities the thermal inertia for the gusev plains rock target bonneville beacon 1200 j m 2 k 1 s 1 2 is consistent with a dense basaltic rock but the rocks at the columbia hills have a lower thermal inertia 620 j m 2 k 1 s 1 2 suggesting that they have a volcaniclasic origin bedforms on the floors of craters at both landing sites have thermal inertias of 200 j m 2 k 1 s 1 2 consistent with a particle diameter of 160 m this diameter is comparable to the most easily moved grain size in the current atmosphere on mars suggesting that these bedforms may have formed under current atmospheric conditions along the meridiani plains the thermal inertia is lower than that derived from tes and thermal emission imaging system themis orbital data this discrepancy is not well understood mini tes derived thermal inertias at gusev along a 2 5 km traverse follow trends in thermal inertia measured from orbit with tes and themis however along the traverse there are variability and mixing of particle sizes that are not resolved in the orbital thermal inertia data due to meter scale processes that are not identifiable at larger scales

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

ma adim vallis evolution geometry and models of discharge rate abstract episodes of confined flows in ma adim vallis are reconstructed by surveying the terraces in the valley three major levels and their associated tributary systems are identified and mapped this study points out the evidence of the cessation of the valley activity between the formation of levels 1 and 2 characterized by degraded and large perched valleys which floor are not adjusted to the following flow episode level a strong asymmetry in the tributary distribution points toward a groundwater supplied water origin of the valley potential source areas are demonstrated to be in volcano tectonic regions implying a hydrothermal origin of the water that may include melted permafrost calculation of hydraulic radii valley sections and models of discharge rates associated with the morphologic and geologic survey shows that ma adim vallis was an episodic channel the lifetime of which spanned between the noachian and amazonian

active dust devils in gusev crater mars observations from the mars exploration rover spirit 1 a full dust devil season was observed from spirit from 10 march 2005 sol 421 first active dust devil observed to 12 december 2005 sol 691 last dust devil seen this corresponds to the period ls 173 2 to 339 5 or the southern spring and summer on mars thermal emission spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in gusev and that spirit landed in the waning stages of a dust devil season as temperatures decreased 533 active dust devils were observed enabling new characterizations they ranged in diameter from 2 to 276 m with most in the range of 10 20 m in diameter and occurred from about 0930 to 1630 hours local true solar time with the maximum forming around 1300 hours and a peak occurrence in southern late spring ls 250 horizontal speeds of the dust devils ranged from 1 to 21 m s while vertical wind speeds within the dust devils ranged from 0 2 to 8 8 m s these data when combined with estimates of the dust content within the dust devils yield dust fluxes of 3 95 10 9 to 4 59 4 kg m2 s analysis of the dust devil frequency distribution over the inferred dust devil zone within gusev crater yields 50 active dust devils km2 sol suggesting a dust loading into the atmosphere of 19 kg km2 sol this value is less than one tenth the estimates by cantor et al 2001 for regional dust storms on mars

hemoilmenite as a carrier of srtrm in dacitic pumice from akagi ontake and sambe volcanoes japan abstract hemoilmenite crystals 0 7 x 0 4 x ilmenite molecular fraction in ilmenite hematite solid solution series in dacite pumice in japanese arc volcanoes are common however only a small percentage of those pumices show classic self reversed thermo remanent magnetization srtrm such as that first found in a haruna dacite pumice the dacite pumice samples from akagi volcano in central japan about 110 km nw of tokyo n36 33 e139 12 however acquired an intense srtrm like that of the haruna volcano samples bitter patterns of the oriented hemoilmenite crystals from both the haruna and akagi volcanoes indicate that ordered ferrimagnetic and disordered weak ferromagnetic phases are inter grown in relatively comparable amounts with an irregular texture this pattern is consistent with rapid quenching of these pumices we conclude that not only the chemical composition tio 2 content or x of the hemoilmenite but also the cooling speed or thermal condition on cooling control srtrm acquisition in hemoilmenite of appropriate composition

micromagnetic rockmagnetic and mineralogical studies on dacitic pumice from the pinatubo eruption 1991 phillipines showing self reversed trm detailed micromagnetic rockmagnetic and mineralogical investigations on dacitic pumice from the eruption of mt pinatubo 1991 phillipines showing reversed nrm trm are presented two intergrown hemoilmenite phases in chemically zoned particles were detected as being responsible a rim or covering phase consisting of a weak ferromagnetic disordered hemoilmenite phase low saturation magnetization but magnetically hard like hematite fetio 3 content 53 57 mol percent and a core phase consisting of a ferrimagnetic ordered hemoilmenite phase high saturation magnetization but magnetically softer constant fetio 3 content 58 mol percent preliminary studies were carried out in order to elucidate the magnetic interactions possibly exchange coupling responsible for the self reversal of the nrm trm a preliminary and schematic model is presented which summarizes the main points of acquisition of a self reversed trm according to out results

low temperature behavior and memory of iron rich titanomagnetites mt haruna japan and mt pinatubo philippines we report low temperature remanence and memory of octahedral crystals of titanomagnetite from mt haruna japan and mt pinatubo philippines the crystals have curie temperatures of 460 490 c indicating a low ti content 0 11 x 0 16 saturation isothermal remanence sirm produced at 20 k decreased rapidly in warming through the isotropic temperature 42 k ti 55 k where the first magnetocrystalline anisotropy constant k1 changes sign and momentarily vanishes 96 99 of the original sirm was demagnetized at ti and none was recovered in recooling from 300 k to 20 k sirm produced at 300 k decreased continuously in the course of zero field cooling leveling out around ti on rewarming to 300 k 45 60 of the initial sirm was recovered this memory or recovered remanence is very large compared to that of magnetite and must be due to domain walls that are more strongly pinned probably magnetostrictively by crystal defects which are common in natural crystals the present low temperature experiments provide a quick non destructive method of identifying iron rich titanomagnetites in soils sediments and rocks

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

self reversal explanation for the laschamp olby geomagnetic field excursion abstract the reversed natural remanent magnetisation nrm of the volcanic features at laschamp and olby chaine des puys auvergne france is commonly believed to document the youngest excursion of the geomagnetic field during the present brunhes epoch recent radiometric dating determines the age of these lavas to be 35000 45000 y continuous thermal demagnetisation indicates that under laboratory conditions the nrm of many olby samples undergoes complete or partial self reversal to a lesser extent this is also true for the laschamp material thus self reversal may be another possible explanation of the reversed nrm directions magnetic optical and microprobe analyses suggest that the self reversal mechanism is based upon magnetostatic interaction between differently oxidised titanomagnetite phases

two phase opening model for the okinawa trough inferred from paleomagnetic study of the ryukyu arc tertiary volcanic and sedimentary rocks were collected at 50 sites of both the central ryukyu arc and the southern ryukyu arc for a paleomagnetic and geochronological study in an attempt to understand the opening of the okinawa trough back arc basin stable primary components of remanent magnetization were isolated through both thermal and alternating field demagnetization experiments from 12 sites of three geological units of the central ryukyu arc and from 12 sites of two geological units of the southern ryukyu arc the paleomagnetic results were compared with the tertiary apparent pole wander path of eurasia in order to investigate the tectonic movement of the ryukyu arc with respect to the asian continent the comparison and the radiometric ages indicate that the southern ryukyu arc rotated clockwise through 25 between 10 ma and 6 ma in contrast the central ryukyu arc experienced little rotational motion since 17 ma we propose the following two phase opening model for the okinawa trough opening the first stage took place between 10 ma and 6 ma the southern part of the trough opened by means of a wedge mode to cause the clockwise rotation of the southern ryukyu arc in the central part the parallel opening occurred and the ryukyu arc drifted without any rotation the second phase started recently in the whole okinawa trough it is observed as the present activities in the trough

anomalously shallow palaeomagnetic inclinations and the question of the age of the canarian archipelago summary extensive geological geophysical and geochronological data available from the canary islands establish conclusively that formation of the oldest subaerial volcanic structure of the islands began during the miocene a mid cretaceous age for these volcanic formations has been postulated in previous works on the basis of palaeomagnetic determinations the results obtained in the present palaeomagnetic study of lanzarote include analysis of the record of variations of magnetic inclination in boreholes that penetrate the whole of the oldest volcanic series they show that the excessive age previously assigned to these formations is due to the utilization of volcanic units with abnormally low 15 magnetic inclinations lgis in lanzarote lavas exhibiting lgis appear interbedded in a volcanic series that overall shows a typical miocene inclination 45 the units stratigraphically beneath and above the lgi horizons give in fact directions consistent with the middle upper miocene field direction d 359 i 45 with k 29 a95 6 7 and a palaeopole of 87 n 178 e thereby confirming the miocene age of the oldest subaerial volcanics of lanzarote short excursions of the geomagnetic field seem likely to be the explanation for these lgis since other factors such as tectonic tilting post eruptive modification of the primary remanence or errors in sample orientation can be disregarded the detection in the canary archipelago of volcanic units with abnormally low magnetic inclinations seems to be related to the relatively continuous record of the geomagnetic field in rapidly growing volcanic edifices as seems to be indicated by the presence of a few usually one or two short polarity events in volcanic suites of several hundred metres thickness

soil sedimentology at gusev crater from columbia memorial station to winter haven 1 a total of 3140 individual particles were examined in 31 soils along spirit s traverse their size shape and texture were quantified and classified they represent a unique record of 3 years of sedimentologic exploration from landing to sol 1085 covering the plains unit to winter haven where spirit spent the martian winter of 2006 samples in the plains unit and columbia hills appear as reflecting contrasting textural domains one is heterogeneous with a continuum of angular to round particles of fine sand to pebble sizes that are generally dust covered and locally cemented in place the second shows the effect of a dominant and ongoing dynamic aeolian process that redistributes a uniform population of medium size sand the texture of particles observed in the samples at gusev crater results from volcanic aeolian impact and water related processes

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

remanent magnetization of andesitic and dacitic pumice from the 1985 eruption of nevado del ruiz colombia reversed due to self reversal the natural remanent magnetization of andesitic pumice emitted during the 1985 eruption of the nevado del ruiz volcano colombia has a direction opposite to the present geomagnetic field the self reversing mechanism can be re activated in the laboratory during cycles of heating and subsequent cooling in air and zero magnetic field laboratory produced thermoremanent magnetization is dominated by the same self reversal process in fields up to several mt microchemical optical and curie temperature analyses indicate that the ferromagnetic minerals are members of the magnetite ulvospinel and hematite ilmenite series with average compositions of fe2 73ti0 27o4 and fe1 38ti0 62o3 respectively in analogy with the magnetic behaviour of synthetically grown antiferromagnetic ferromagnetic femn feni films the self reversal can probably be interpreted in terms of an exchange field acting between a ti poor canted antiferromagnetic and a ti rich ferrimagnetic phase in the hemoilmenite grains

low temperature partial magnetic self reversal in marine sediments by magnetostatic interaction of titanomagnetite and titanohematite intergrowths with various low temperature experiments performed on magnetic mineral extracts of marine sedimentary deposits from the argentine continental slope near the rio de la plata estuary a so far unreported style of partial magnetic self reversal has been detected in these sediments the sulphate methane transition smt zone is situated at depths between 4 and 8 m where reductive diagenesis severely alters the magnetic mineral assemblage throughout the sediment column magnetite and ilmenite are present together with titanomagnetite and titanohematite of varying compositions in the smt zone titano magnetite only occurs as inclusions in a siliceous matrix and as intergrowths with lamellar ilmenite and titanium rich titanohematite originating from high temperature deuteric oxidation within the volcanic host rocks these abundant structures were visualized by scanning electron microscopy and analysed by energy dispersive spectroscopy warming of field cooled and zero field cooled low temperature saturation remanence displays magnetic phase transitions of titanium rich titanohematite below 50 k and the verwey transition of magnetite a prominent irreversible decline characterizes zero field cooling of room temperature saturation remanence it typically sets out at 210 k and is most clearly developed in the lower part of the smt zone where low temperature hysteresis measurements identified 210 k as the blocking temperature range of a titanohematite phase with a curie temperature of around 240 k the mechanism responsible for the marked loss of remanence is therefore sought in partial magnetic self reversal by magnetostatic interaction of titano magnetite and titanohematite when titanohematite becomes ferrimagnetic upon cooling its spontaneous magnetic moments order antiparallel to the titano magnetite remanence causing an drastic initial decrease of global magnetization the loss of remanence during subsequent further cooling appears to result from two combined effects 1 magnetic interaction between the two phases by which the titano magnetite domain structure is substantially modified and 2 low temperature demagnetization of titano magnetite due to decreasing magnetocrystalline anisotropy the depletion of titanomagnetite and superior preservation of titanohematite is characteristic for strongly reducing sedimentary environments typical residuals of magnetic mineral assemblages derived from basaltic volcanics will be intergrowths of titanohematite lamellae with titanomagnetite relics low temperature remanence cycling is therefore proposed as a diagnostic method to magnetically characterize such alteration palaeo environments 2007 the authors journal compilation 2007 ras