chemical and physical studies of type 3 chondrites ix thermoluminescence and hydrothermal annealing experiments and their relationship to metamorphism and aqueous alteration in type 3 3 ordinary chondrites samples of four type 3 chondrites have been annealed at 400 850 c and 0 77 1 kbar for 10 500 h in the presence of various amounts of water 0 10 wt and sodium disilicate 0 2 molal and their thermoluminescence properties measured after annealing for 20 h at temperatures 600 c the tl sensitivity of the samples increased by factors of up to 40 after annealing at 800 c when both high and low forms were present originally the low form was destroyed preferentially we suggest that these data are consistent with the tl metamorphism trends observed in type 3 2 chondrites being due to the formation of feldspar with structural details being dependent on formation temperature by the devitrification of chondrule glass during metamorphism for types 3 2 the tl data are equally consistent with these types experiencing lower levels of metamorphism than the higher types or with type 3 0 being produced from higher types by aqueous alteration the presence of water with non terrestrial d h ratios and petrographic evidence for aqueous alteration in semarkona lead us to favour the aqueous alteration hypothesis

petrology trace element abundances and oxygen isotopic compositions of a compound cai chondrule object from allende abstract we report the petrology trace element abundances and oxygen isotopic characteristics of a compound cai chondrule object wi 025 found in the allende cv3 chondrite the wi 025 is an irregularly shaped inclusion consisting of three texturally and chemically distinct portions the interior portion the igneous rim and the intermediate zone located between these two portions the interior portion consists of anorthite spinel olivine and al bearing low ca pyroxene the major element chemistry of the interior portion corresponds to that of al rich chondrules and is of intermediate character between fine grained spinel rich cais and ferromagnesian chondrules the interior portion has abundant 16 o rich spinel 17 o 14 2 to 24 7 and displays a group ii cai like ree composition these observations indicate that the interior portion contains a cai component formed by fractional condensation the major and trace element chemistry of the interior portion indicate that the cai had subsequently assimilated chondrule materials through partial melting the maximum heating temperature of the partial melting is estimated at approximately 1400 c similar to the maximum heating temperature of type b cais the oxygen isotopic compositions of the olivine and low ca pyroxene 17 o 6 3 in the interior portion indicate that the partial melting and chondrule assimilation took place under a moderately 16 o poor nebular gas the igneous rim is texturally and chemically similar to ferromagnesian chondrules and entirely surrounds the interior portion the oxygen isotopic compositions of the olivine and low ca pyroxene in the igneous rim are indistinguishable from those of the interior olivine and al bearing low ca pyroxenes these observations indicate that a chondrule material which was melted in the same nebular gas as the interior portion was accreted to the interior portion the intermediate zone represents a reaction zone accompanying the igneous rim formation the formation history of wi 025 can be summarized by the following processes 1 original cai formation 2 partial melting and chondrule assimilation 3 igneous rim formation and 4 secondary alteration on the parent body

erosional valleys in the thaumasia region of mars hydrothermal and seismic origins analysis of erosional valleys geologic materials and features and topography through time in the thaumasia region of mars using co registered digital spatial data sets reveals significant associations that relate to valley origin valleys tend to originate 1 on noachian to early hesperian stages 1 and 2 large volcanoes 2 within 50 100 km of stages 1 and 2 rift systems and 3 within 100 km of noachian stage 1 impact craters 50 km in diameter these geologic preferences explain observations of higher valley source densities vsds in areas of higher elevations and regional slopes 1 because the volcanoes rifts and craters form high steep topography or occur in terrain of high relief other stage 1 and stage 2 high steep terrains however do not show high vsds the tendency for valleys to concentrate near geologic features and the overall low drainage densities in thaumasia compared to terrestrial surfaces rule out widespread precipitation as a major factor in valley formation as is proposed in wann wet climate scenarios except perhaps during the early noachian for which much of the geologic record has been obliterated instead volcanoes and rifts may indicate the presence of shallow crustal intrusions that could lead to local hydrothermal circulation melting of ground ice and snow and groundwater sapping however impact crater melt would provide a heat source at the surface that might drive away water fonning valleys in the process post stage 1 craters mostly have low nearby vsds which for valleys incised in older rocks suggests burial by ejecta and for younger valleys may indicate desiccation of near surface water and deepening of the cryosphere later hesperian and amazonian stages 3 and 4 valleys originate within 100 200 km of three young large impact craters and near rifts systems at warrego valles and the southern part of coprates rise these valleys likely developed when the cryosphere was a couple kilometers or more thick inhibiting valley development by hydrothermal circulation however eruption of groundwater may have occurred from impact induced fracturing and lateral and perhaps minor upward transport of water due to seismic pumping the two smaller craters formed along the plateau margin where the highest potential hydraulic head would occur in aquifers beneath the plateau in the case of the larger crater lowell 200 km in diameter potential aquifers would likely be at depths of kilometers below the cryosphere seismic energy generated by the lowell impactor would have been much greater pumping both groundwater and perhaps fluidized slurry to the surface from beneath the cryosphere to form the young valleys and flow deposit along the margin of thaumasia tectonic pressurization of groundwater also may have contributed to valley formation dissection of rim materials of the argyre impact may relate to tectonic activity and the unconsolidated state of basin ejecta

cumberland falls chondritic inclusions iii consortium study of relationship to inclusions in allan hills 78113 aubrite abstract we describe the mineralogy and report contents of ag au bi cd co cs ga in rb sb se te tl u and zn determined by rnaa in three primitive chondritic inclusions from the alh a78113 aubrite comparison of these data with those for large petrologic type 3 chondritic clasts from the cumberland falls aubrite and the discovery of small clasts in it like those in alh a78113 indicate that all constitute a single chondritic suite we also report thermoluminescence data for cumberland falls chondritic inclusions and achondritic host these results together with mineralogie major minor and trace element information demonstrate that aubrite inclusions represent a different sort of type 3 chondrite not an ll3 chondrite altered during equilibration with aubrite host instead the aubrite inclusions represent a distinct chondrite class these inclusions reflect nebular condensation accretion over a broad redox range and at temperatures relatively high compared with those at which other type 3 chondrites formed limited metamorphism and reduction occurred during condensation accretion prior to incorporation into aubrite host during the impact of the chondritic parent body with the aubrite parent body chondrite fragments were strongly shocked and cooled rapidly they then mixed with aubrite host possibly in a regolith so that these aubrites now represent impact breccias

origin of sio2 rich components in ordinary chondrites abstract silica rich objects are common minor components in ordinary chondrites oc occurring as fragments and as chondrules their typical paragenesis is orthopyroxene sio 2 with bulk sio 2 65 wt and occasionally with additional olivine and or spinel individual silica rich components src have previously been studied in various types of ocs although there is only one comprehensive study of these objects by brigham et al brigham c a murrell m t yabuki h ouyang z el goresy a 1986 silica bearing chondrules and clasts in ordinary chondrites geochim cosmochim acta 50 1655 1666 several different explanations of how srcs formed have been published the main question is how silica enrichment was achieved because ci chondritic atomic mg si ratio is 1 07 and as a consequence only olivine and pyroxene but no free silica should be stable there are two basic possibilities for the sio 2 enrichment 1 a redox mechanism or magmatic fractionation on the parent body and 2 fractional condensation or recycling of chondrule mesostasis in the solar nebula to better constrain the origin of these objects we measured major and rare earth elements in srcs of various types of ordinary chondrites and in addition we studied silica polymorphism in these objects using an in situ micro raman technique bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene the srcs extend these lines to an sio 2 end member in contrast magmatic trends grossly deviate from these mixing lines concentrations of cao al 2 o 3 and ree in the pyroxenes of the srcs are low 0 01 to 1 ci and the ci normalized ree patterns are virtually flat typical of bulk chondrules but untypical of magmatic trends we therefore conclude that sio 2 rich objects are not of magmatic origin they are the result of fractional condensation in the solar nebula the silica in srcs occurs mainly as tridymite and sometimes as cristobalite or in very rare cases as quartz some sio 2 phases yielded a yet unknown micro raman spectrum which we were unable to identify the often chondrule like shape of srcs as well as the presence of high temperature sio 2 polymorphs lead to the following model for the origin of srcs formation of sio 2 rich precursors in the solar nebula by fractional condensation reheating to temperatures between 1140 and 1968 k thereby forming the srcs probably during the chondrule forming process followed by rapid cooling

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

orographic precipitation in valley network headwaters constraints on the ancient martian atmosphere 1 we examine the martian valley networks in the framework of topographic influences on precipitation we use an analytical model and the laboratoire de meteorologie dynamique lmd early mars global circulation model gcm to explore the local scale distribution of orographically forced precipitation as a function of atmospheric pressure in simulations with 500 mbar and 1 bar co2 atmospheres orographic lifting results in enhanced snowfall upslope of the observed valley network tributaries our framework also suggests that a 2 bar atmosphere cannot create the observed valley pattern at the highest relief valley network warrego valles as in previous work the gcm does not generate temperatures warm enough for rain or significant snowmelt in the highlands with co2 greenhouse warming alone thus while transient periods of unusual warming are still required to melt the deposits and carve the valleys our model predicts snow deposition in the correct locations

fractal analysis of drainage basins on mars 1 we used statistical properties of drainage networks on mars as a measure of martian landscape morphology and an indicator of landscape evolution processes we utilize the mars orbiter laser altimeter mola data to construct digital elevation maps dems of several mostly ancient martian terrains drainage basins and channel networks are computationally extracted from dems and their structures are analyzed and compared to drainage networks extracted from terrestrial and lunar dems we show that martian networks are self affine statistical fractals with planar properties similar to terrestrial networks but vertical properties similar to lunar networks the uniformity of martian drainage density is between those for terrestrial and lunar landscapes our results are consistent with the roughening of ancient martian terrains by combination of rainfall fed erosion and impacts although roughening by other fluvial processes cannot be excluded the notion of sustained rainfall in recent mars history is inconsistent with our findings

rotary sidescan images of nearshore bedform evolution during a storm abstract high resolution acoustic images are presented of bedform development on the crest of a nearshore bar during a storm the images were obtained using a 2 25 mhz rotating sidescan sonar the sonar system provides a continuous record of the evolution of the bedform field through time within a 10 m diameter field of view the images document the occurrence of ripples cross ripples and megaripples during the waning stages of the storm transitions among ripple types occurred on time scales of 1 3 h beginning with flat bed and culminating in highly 3 d short crested ripples

topographic influences on development of martian valley networks 1 some morphometric differences between terrestrial and martian valley networks may reflect the precursor topography on mars particularly impact basins or tectonic slopes to evaluate these possible influences we mapped highland watersheds in nine study areas that sample a range of geographic and topographic settings we collected data including latitude longitude watershed length divide and terminal elevations watershed relief and slope slope orientation and qualitative descriptors including whether a drainage basin was open or closed the longest valley networks and most overflowed basins occur on preexisting intercrater slopes of 0 1 1 particularly on north facing slopes associated with the crustal dichotomy the control of watershed length by earlier noachian topographic features which the relict networks did not significantly modify suggests that the early to middle noachian geomorphic environment was nominally much drier than the later noachian to hesperian transition the distribution of fluvial valleys and likely orographic effects created by the crustal dichotomy suggest that evaporation from the northern lowlands was an important source of atmospheric humidity over short time scales much of the highland plateau consists of smaller enclosed watersheds which along with cooler temperatures detained surface water at high elevations lengthening or impeding the global water cycle ponding and evaporation may have partly offset a continentality effect of the highland landmass prolonged modification of the intercrater geomorphic surface prior to incision of valley networks included substantial weathering reduction of relief and gravity driven sediment transport indicating a long term role for surface water in a transport limited arid to hyperarid noachian paleoclimate

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

chemical and physical studies of type 3 chondrites i metamorphism related studies of antarctic and other type 3 ordinary chondrites abstract thermoluminescence sensitivity measurements have been made on 18 unequilibrated ordinary chondrites 12 finds from antarctica 5 non antarctic finds and 1 fall the tl sensitivities of these meteorites normalized to dhajala range from 0 034 st mary s county to 2 3 allan hills a78084 and based primarily on these data petrologic type assignments range from 3 3 st mary s county to 3 9 allan hills a78084 although the very low levels of metamorphism experienced by types 3 0 to 3 4 evidently cause large changes in tl sensitivity the new data demonstrate that they are unable to cause any appreciable homogenization of silicate compositions we have therefore slightly revised the silicate heterogeneity ranges corresponding to the lower petrologic types we have discovered that the temperature of maximum tl emission and the broadness of the major tl peak vary systematically with tl sensitivity as tl increases these parameters first decrease and then increase several mechanisms which could account partially or completely for the relationship between tl sensitivity and metamorphism are discussed those which involve the formation of feldspar the tl phosphor in equilibrated meteorites seem to be consistent with the trends in peak temperature and peak width since experiments on terrestrial albite show that the tl peak broadens and moves to higher temperatures as the stable form changes from the low ordered state to the high disordered state the post metamorphism equilibration temperature of type 3 5 meteorites would then correspond to the transformation temperature for the high to low form of meteorite feldspar other factors which may be involved are obscuration of the tl by carbonaceous material changes in the composition of the phosphor and changes in the identity of the phosphor

late alluvial fan formation in southern margaritifer terra mars 1 crater statistics indicate alluvial fans crater floor and fill mantling deposits within impact craters 50 km in diameter in southern margaritifer terra were likely emplaced during multiple epochs fans formed during the amazonian or near the amazonian hesperian boundary crater floor deposits are likely hesperian in age and most fill mantling deposits are amazonian the regional distribution of fans points to a late period of widespread water driven degradation two of the final candidate landing sites for the 2011 mars science laboratory mission would land on or near some of these fans which appear younger than previously considered

outflow channels with deltaic deposits in ismenius lacus mars abstract a connected series of outflow channels in the ismenius lacus quadrangle are identified for the first time and characterized using high resolution stereo camera images of mars express the context camera images of mars reconnaissance orbiter and the topography of the mars observer laser altimeter these channels named okavango valles which stretch over 400 km south to north and join the northern plains were identified from braided channels scour groove marks poorly sinuous valleys and depositional landforms discharge rates were estimated to 0 1 5 10 6 m 3 s 1 from analysis of the topography of scour marks pathways of channels segments were extracted from topography showing a unique source at a breached crater rim suggesting overflow from ponded depressions a series of delta fans are observed inside depressions along the channel pathways the presence of these deltas formed in former bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows the similarity of these flows with other outflow channels on mars proves that volcanically related outflows cannot explain all such features in addition this study also shows that catastrophic floods are able to create fan deltas in transient lakes this example has to be taken into account in the interpretation of late stage fans associated with poorly branched valleys and single channels

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

sand bed roughness in the nearshore 1 measurements made using sonar altimeters mounted on an amphibious surveying vehicle are analyzed for root mean square rms bedform roughness observations for 22 days over a 500 m 700 m area are used to quantify the cross shore distribution of roughness and its variability large bedforms with amplitudes 5 50 cm occur frequently in shallow water 2 m water depth however the patchiness of these bedforms is also largest in shallow water this is likely owing to the spatial and temporal variability of the waves and currents of the sediment grain size distributions and of the large scale nearshore morphology large bedforms were observed to exist only for mobility numbers 150 above this threshold the rms roughness was 2 cm and the bed was interpreted to have transitioned to sheet flow conditions however the state of the bed e g large ripples small ripples flat bed was not predictable for mobility numbers between about 30 and 150 existing models for orbital ripples do not predict the observed large bedforms and have little predictive skill for these data

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

chemical and physical studies of type 3 chondrites iii chondrules from the dhajala h3 8 chondrite abstract fifty eight chondrules were separated from the dhajala h3 8 chondrite and their thermoluminescence properties were measured chips from 30 of the chondrules were examined petrographically and with electron microprobe techniques the bulk compositions of 30 chondrules were determined by the fused bead technique porphyritic chondrules especially 5 which have particularly high contents of mesostasis tend to have higher tl mass normalized than non porphyritic chondrules significant correlations between log tl and the bulk cao al 2 o 3 and mno content of the chondrules and between log tl and the cao al 2 o 3 sio 2 and normative anorthite content of the chondrule glass indicate an association between tl and the abundance and composition of mesostasis unequilibrated chondrules i e those whose olivine is compositionally heterogeneous and high in ca have low tl whereas equilibrated chondrules have a wide range of tl depending on their chemical and petrographic properties we suggest that the tl level in a given chondrule is governed by its bulk composition which largely determined the abundance and composition of constituent glass and by metamorphism which devitrfied the glass in those chondrules with high ca glass to produce the tl phosphor we also suggest that one reason why certain chondrules in type 3 ordinary chondrites are unequilibrated while others are equilibrated is that the mesostasis of the unequilibrated chondrules resisted the devitrification this devitrification is necessary for the diffusive communication between chondrule grains and matrix that enables equilibration

extraction of martian valley networks from digital topography 1 we have developed a novel method for delineating valley networks on mars the valleys are inferred from digital topography by an autonomous computer algorithm as drainage networks instead of being manually mapped from images individual drainage basins are precisely defined and reconstructed to restore flow continuity disrupted by craters drainage networks are extracted from their underlying basins using the contributing area threshold method we demonstrate that such drainage networks coincide with mapped valley networks verifying that valley networks are indeed drainage systems our procedure is capable of delineating and analyzing valley networks with unparalleled speed and consistency we have applied this method to 28 noachian locations on mars exhibiting prominent valley networks all extracted networks have a planar morphology similar to that of terrestrial river networks they are characterized by a drainage density of 0 1 km 1 low in comparison to the drainage density of terrestrial river networks slopes of streams in martian valley networks decrease downstream at a slower rate than slopes of streams in terrestrial river networks this analysis based on a sizable data set of valley networks reveals that although valley networks have some features pointing to their origin by precipitation fed runoff erosion their quantitative characteristics suggest that precipitation intensity and or longevity of past pluvial climate were inadequate to develop mature drainage basins on mars

cross shore migration of lunate megaripples during duck94 1 remote acoustic observations of lunate megaripple migration are presented from two storm events during the duck94 nearshore dynamics experiment for time periods during which longshore currents were weak 20 cm s during these periods significant wave orbital velocities were 50 80 cm s megaripple heights were 0 05 0 5 m megaripple horns were directed shoreward the crest to trough slope of the shoreward advancing ripple face was close to the angle of repose and migration speeds were 10 40 cm h onshore the observations also indicate that the megaripples stalled and may have begun to migrate offshore when the mean offshore flow exceeded 20 cm s during the second storm stress based bed load sediment transport models are moderately successful in predicting the observed dependence of migration velocity on measured fluid velocities separated into zero mean current infragravity wave and sea and swell wave frequency bands wave and mean current friction factors fw and fc are obtained by best fit between the predicted and observed migration velocities for two choices 3 2 and 5 2 for the stress exponent in the bed load transport part of the model net transport is computed using wave velocity amplitudes determined from both run length statistics and wave by wave improved agreement with observations is obtained for the wave by wave net transport predictions and for the wave like treatment of the infragravity band the level of agreement is relatively insensitive to the value of the best fit current and wave friction factor values for 5 2 and 3 2 are fc 4 3 10 3 and 8 0 10 3 and fw 1 7 10 2 and 4 8 10 2 respectively

observations of event scale sedimentary dynamics with an instrumented bottom boundary layer tripod abstract a new approach to examine event scale sedimentation is described that establishes a direct connection between water column signals and changes in the seabed the po river italy shelf is a good case study due to the dominant impact of winter storm events on sediment transport and the availability of coincident measurements necessary for the analysis repeated deployments of an instrumented bottom boundary layer tripod at this site have produced a nearly continuous record of sediment transport over 2 5 y sediment cores were collected every 3 mo during this time and seabed inventories of 7 be half life 53 3 d were used to determine net sediment deposition or erosion during each deployment comparison of these values with the net elevation change obtained from the tripod altimeter shows good agreement varying from 2 cm deposition to 1 cm erosion the altimeter s use is extended to quantify the net seabed change that results from individual storm induced sediment resuspension events lasting from days to weeks within each event analysis of the altimeter record has proved challenging likely due to changes in sediment porosity that occur during a storm event however net erosion and deposition that occurs over an event can be evaluated and was found to be

metal and associated phases in bishunpur a highly unequilibrated ordinary chondrite it appears that the highly unequilibrated bishunpur ordinary chondrite preserves phase relations acquired during solar nebular processes to a relatively high degree metamorphic temperatures may not have exceeded 300 350 c the major categories of metal are 3 kinds of metal in the metal matrix three kinds in chondrule interiors and 2 kinds in chondrule rims the fine grained matrix metal is highly variable in composition the kamacite co content 7 8 2 0 mg g is within the l group range 6 7 8 2 mg g but extends well above and below its ni content 38 5 mg g is considerably lower than in more equilibrated chondrites and taenite is ni rich 450 mg g and unzoned these compositions imply equilibration at very low temperatures of about 300 350 c it seems unlikely that volume diffusion could account for the observed relatively unzoned phases a better model involves mass transport by grain boundary diffusion and grain growth at the indicated temperatures we find no evidence that the matrix was ever at higher temperatures large 50 650 m polycrystalline metal aggregates consisting of individually zoned crystals are also found in the matrix they probably represent clusters formed in the solar nebula a few large 50 250 m round monocrystalline grains are also present in the matrix metal bearing chondrules tend to be highly reduced they contain low ni metal that occasionally contains si and or cr silicates in these chondrules tend to have low feo feo mgo ratios the si rich metal grains are never in contact with silicates and are always surrounded by troilite with a poorly characterized ca cr sulfide at the metal troilite interface they appear to be high temperature nebular condensates that avoided oxidation even during the chondrule forming process silicon contents drop below our detection limit when the sulfide coating is absent much more common in chondrule interiors are si free spheroidal metal grains not associated with sulfides these have ni and co contents very similar to the si bearing grains and appear to be oxidized variants of the same material the third class of chondrule metal is fine 1 m dusty grains inside individual olivine grains these seem to reflect high temperature in situ reduction of feo from the olivine the composition of kamacite is different in sulfide rich and sulfide poor chondrule rims and in both cases it is dissimilar to the compositions in the chondrule interiors and matrix this indicates that chondrule rims could not have resulted from reactions with the matrix but are primary features acquired prior to accretton

crossover analysis of mars orbiter laser altimeter data in its first 15 months of continuous operation the mars orbiter laser altimeter mola instrument aboard mars global surveyor ranged to mars over 330 million times generating more than 5000 orbital profiles with a ranging precision of 0 4 m over smooth terrain the accuracy of the profiles depends on knowledge of the spacecraft position orientation and observation time which are subject to errors we model these errors via the analysis of over 24 million altimetric crossovers a quasiperiodic once per revolution adjustment of the ground tracks as a function of time in three locally orthogonal directions minimizes the altimetric residuals via least squares using a sparse matrix technique computational effort scales linearly with the number of crossovers and only marginally with the number of parameters orbital errors mainly result from poor modeling of spacecraft thrusting events in the absence of tracking seasonal effects likely due to changing thermal environment as well as residual miscalibrations are evident in the pointing solutions incorporating multiple parameters per revolution significantly improves crossover residuals and resolves pointing aberrations during orbital transitions from night to day altimetry from the adjusted tracks generates a topographic model whose accuracy is typically better than 1 m vertically with respect to the center of mass of mars the centroid position of each mola shot is typically accurate to 100 m horizontally terrain models from accurately located lidar data can be gradient shaded to illuminate geological structures with 1 in 1000 slopes that are invisible to cameras temporal changes in elevation e g frost deposition ablation at decimeter levels may also be assessed using crossovers but results must be interpreted with caution due to uncertainties in range walk correction

geometric bed roughness and the bed state storm cycle 1 temporal variation in the geometric roughness of the mobile sandy seabed during wave forcing events is investigated as a function of bed state the bed states include irregular ripples cross ripples linear transition ripples and flat bed each appearing repeatedly within a different range of wave energies as part of the bed state storm cycle ripple wavelengths determined from ensemble averaged roughness spectra indicate that irregular and cross ripples are suborbital whereas linear transition ripples are anorbital the observed ripple steepnesses indicate that irregular and linear transition ripples fall slightly below nielsen s 1981 field data relation whereas cross ripple steepnesses are anomalously low in comparison time series of geometric roughness are coherent across spatial frequency abrupt changes in geometric roughness occurred on timescales of 3 h on average during both the onset and the waning stages of storm events i e for both decreasing and increasing roughness respectively predicted response times based on ripple volume and bed load transport rate are in agreement with the observations when the best fit form of the meyer peter and muller 1948 type bed load relation obtained by ribberink 1998 is used in contrast the more standard form of this relation and the associated parameters yield predicted response times much shorter than those observed

chemical and physical studies of type 3 chondrites 2 thermoluminescence of sixteen type 3 ordinary chondrites and relationships with oxygen isotopes thermoluminescence tl sensitivity values for sixteen type 3 ordinary chondrites fourteen of them from antarctica have been measured the values obtained normalized to the tl sensitivity of the dhajala meteorite range from 1 6 allan hills a77216 to 0 010 allan hills a77176 and include two reckling peak a80207 and allan hills a77176 that are particularly low they fill a hiatus in the tl distribution that previously existed between st mary s county and bishunpur the latter being a meteorite with one of the lowest tl sensitivities known the histogram of tl sensitivity values now shows a single distribution with higher values preferred it resembles the histogram for l chondrites occupying the petrologic types 3 4 5 and 6 there is a tendency for the tl sensitivity of meteorites to decrease as 18o increases equilibrated meteorites have tl sensitivities of 5 50 and 18o 4 5 to 5 0 while the most primitive meteorites with tl 0 01 have 18o 5 7 to 6 2 meteorites with intermediate tl have intermediate 18o theoretically it is possible that the range of 18o values observed may reflect progressive loss of o in the form of co at very low temperatures but very restrictive physical conditions and a complex history seem to be required

graphite magnetite aggregates in ordinary chondritic meteorites aggregates consisting largely of submicrometre graphite and magnetite crystals have been identified in 14 unequilibrated and regolith breccia ordinary chondrites like other primitive components they formed before the meteorites accreted chondrite clasts rich in graphite magnetite occur in three regolith breccias and are a new kind of unequilibrated ordinary chondrite they were probably the source of graphite magnetite aggregates in regolith breccias

the thermoluminescence sensitivity metamorphism relationship in ordinary chondrites experimental data on the mechanism and implications for terrestrial systems hydrothermal annealing experiments have been performed on samples of the sharps meteorite in order to investigate the mechanism responsible for the metamorphism related 105 fold range in the thermoluminescence tl sensitivity in ordinary chondrites duplicate 50 mg samples of meteorite were annealed under the following conditions a 168 h at 785 c and 1 kbar b the same time temperature and pressure but with 2 wt water c 174 h at 855 c and 0 77 kbar with 2 wt water and 2 molal sodium disilicate nadisi d the same time temperature and pressure as the preceding samples but with 10 wt h2o and 2 molal nadisi samples annealed under the first three sets of conditions showed little or no change in their tl sensitivities however the samples annealed with 10 wt water and 2 molal nadisi showed a 3 to 10 fold increase in tl sensitivity and the temperature of the tl peak was suggestive of feldspar in the high temperature form we suggest that these data are consistent with the tl sensitivity metamorphism relationship in ordinary chondrites being due to the formation of the tl phosphor feldspar by the crystallization of chondrule glass

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

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

chemical and physical studies of type 3 chondrites vii annealing studies of the dhajala h3 8 chondrite and the thermal history of chondrules and chondrites abstract samples of the dhajala h3 8 chondrite have been annealed for 10 hours at 600 700 800 900 and 1000 c and at 1000 c for 1 2 20 and 100 h and their thermoluminescence tl properties measured the tl sensitivity decreased by a factor of 2 after annealing at but at higher temperatures fell by an order of magnitude an abrupt increase in the temperature of the tl peak from 172 9 cto231 8 c and a steady increase in the width of the peak from 169 7 cto212 5 c were caused by the annealing treatment the tl phosphor in dhajala is thought to be feldspar predominantly in the high temperature disordered form but the present data indicate that a contribution from the low temperature form is also present and that this low temperature component is converted to the high form by the annealing treatment the low temperature feldspar is located in a few of the chondrules 20 of those separated from the meteorite which are also noteworthy for having high tl sensitivities these chondrules must have suffered greater crystallization of their mesostasis than the other chondrules and equilibrated to lower temperatures it is argued that for compositional reasons their mesostasis constituted less of a barrier to diffusion and therefore equilibration presumably the post metamorphic cooling rate of the meteorite through the stability field of the low form was slow enough to permit some crystallization and the width and temperature of the tl peaks for petrologic types 3 5 3 9 are somehow related to cooling rate based on tl there is no indication of a correlation between petrologic type and cooling rate for types 3 5 3 9 this is not consistent with a simple single internally heated meteorite parent body

cadmium mass fractionation in unequilibrated ordinary chondrites abstract measurements of the isotopic composition of cadmium in whole rock samples of a number of unequilibrated ordinary chondrites have shown the presence of significant fractionation in the abundances of the isotopes some meteorites are enhanced in the light isotopes with respect to a laboratory standard whilst the reverse effect is exhibited in other meteorites the mass fractionation is linear over the range 106 116 within the limits set by experimental error the extent of the mass dependent fractionation varies from 2 1 per mass unit for light isotope enrichment for the ll3 chondrite semarkona to 2 7 per mass unit for thell3 chondrite bishunpur this is the first time that negative mass fractionation has been reported for cadmium in meteoritical material the cause of the fractionation is not known if rayleigh distillation were responsible then some correlation with cd concentration would be expected but this is not observed there does not appear to be a correlation between the magnitude of cadmium fractionation and abundance in whole rock samples of unequilibrated ordinary chondrites

computer simulations of self organized megaripples in the nearshore 1 megaripples are bed forms with heights of 20 50 cm and lengths of 1 10 m that are common in the surf zone of natural beaches they affect sediment transport flow energy dissipation and larger scale hydro and morphodynamics they are thought to be dynamically similar to bed forms in deserts rivers and deeper marine environments here a self organization model similar to models for subaerial bed forms is used to simulate the formation and development of megaripples in the surf zone sediment flux is determined from combined wave and current flows using stream power and bed shear stress formulations as well as a third formulation for transport based on simple rules which represent sheet flow random bed irregularities either imposed or resulting from small variations in transport representing turbulence are necessary seeds for bed form development feedback between the bed and the flow in the form of a shadow zone downstream of a bed form and increasing flow acceleration with elevation over the crests of bed forms alter the transport such that organized bed forms emerge modeled bed form morphology including cross sectional shape and plan view and dynamics including growth and migration are similar to natural megaripples the model can be used to extend the field observations of clarke and werner 2004 which suggest that if conditions remain the same megaripples will continue to grow contrary to many bed form models this model supports the idea that bed form spacing grows continually

chemical and physical studies of type 3 chondrites iv annealing studies of a type 3 4 ordinary chondrite and the metamorphic history of meteorites abstract samples of a type 3 4 chondrite have been annealed at 400 1000 c for 1 200 hours their thermoluminescence properties determined and analyzed for k na mn sc and ca by instrumental neutron activation analysis after annealing at 900 c the samples showed a 50 decrease in tl sensitivity while after annealing at 1000 c it fell to 0 1 0 01 times its unannealed value and loss of na and k occurred the tl and compositional changes resemble those observed for the equilibrated kernouve chondrite after similar annealing treatments except that the sharp tl decrease and element loss occurred at 1100 c this difference is presumably due to petrographic differences in the feldspar of the two meteorites the temperature and the width of the tl peak showed a discontinuous increase after annealing at 800 c peak temperature jumped from 130 to 200 c and peak width increased from 90 to 150 c the activation energies for these tl changes are 7 10 kcal mole similar increases in the tl peak temperature have been reported in tl studies of amelia va albite where they were associated with the low to high temperature transformation however the activation energy for the transformation is 80 kcal mole these changes in tl emission characteristics resemble trends observed in type 3 ordinary chondrites and it is suggested that type 3 3 3 5 chondrites have a low feldspar as tl phosphor and 3 5 have high feldspar as the phosphor thermoluminescence therefore provides a means of palaeothermometry for type 3 ordinary chondrites

sedimentology and morphodynamics of a macrotidal beach pendine sands sw wales abstract the foreshore of pendine sands forms the seaward part of an extensive sandy coastal barrier in a shallow carmarthen bay sw wales the sedimentological features of the macrotidal foreshore reflect a tide induced modification of nearshore wave characteristics as the tide ebbs the breaker height may decrease the surf zone widens and becomes increasingly dissipative and swash backwash velocities diminish a concomitant change from plunging to spilling breakers and increasingly symmetrical swash zone flows are associated with a decreasing beach gradient a zero net transport model demonstrates that the beach profile is self stabilising in the short term and periodic levelling has shown that the beach is in long term equilibrium with prevailing conditions though this does not preclude a significant dynamic response to changing tides and waves the flow regimes of wave generated currents decline as the tide ebbs and normal beach processes do not usually affect the lower foreshore accordingly there is an overall seaward fining of the primary framework component of the sands in more detail this framework component displays a slight seaward coarsening across an upper foreshore dominated by high water swash and surf a rapid seaward fining across the mid foreshore in response to the ebb attenuating swash zone flow velocities and a slight seaward fining across the lower foreshore under the action of nearshore shoaling waves bedforms vary from a swash backwash emplaced flat bed across the upper foreshore to the small ripples of nearshore asymmetric oscillatory flows across the lower foreshore the surface sediment veneer is not representative of the subsurface sediments which form in response partly to fairweather conditions partly to storms the upper foreshore is characterised by swash backwash emplaced plane bedding in fine sands frequently disrupted by bubble cavities the mid foreshore is composed of coarser grained shelly traction clogs arranged as landward and seaward dipping large scale cross bedding and or plane bedding these are probably storm breaker surf deposits the lower foreshore though partially and sometimes totally bioturbated shows landward dipping small scale cross bedding in very fine sands sorted by nearshore shoaling waves tide and storm induced modification of the nearshore flow regimes therefore produces a distinctive shore normal array of sedimentary facies each facies is characterised by diagnostic textural and structural signatures a prograding sequence of such macrotidal deposits would be similar to but more extensive than a comparable microtidal sequence

observations of turbulence within a natural surf zone abstract here the reynolds stresses u w and w where u and w are the cross shore alongshore and vertical turbulence velocities respectively and the angle brackets represent time averaging are used to diagnose turbulence dynamics beneath natural breaking surf zone waves the data were collected at truc vert beach france during a 12 day period in 1 3 m water depth with strong cross shore and alongshore currents under high energy wave conditions offshore significant wave heights ranged between 2 and 8 m the u w term is predominantly negative increases with the ratio of wave height hs to water depth h degree of wave breaking and decreases in magnitude toward the bed this supports the view that the cross shore shear stress is due to breaking induced vortices that transport high speed cross shore flow downward and disintegrate close to the bed the occasional positive sign of u w within the lower 15 20 of the water column indicates that sometimes surface generated turbule

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

effects of obliquity and water vapor trace gas greenhouses in the early martian climate 1 we explore possible mechanisms for the generation of warm wet climates on early mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions the presence of both water vapor a strong greenhouse gas and other trace greenhouse gases such as so2 in a predominantly co2 atmosphere may act under certain conditions to elevate surface temperatures above the freezing point of liquid water at least episodically variations in obliquity are explored to investigate whether these periodic variations in insolation at mars can broaden the regions or seasons where warm temperatures can exist we use the mars weather research and forecasting general circulation model to perform several simulations of the conditions of the early martian atmosphere containing these gases and find global temperatures to be cooler than the elevated levels suggested by at least one recent study by johnson et al 2008 while achieving temperatures above 273 k globally remains challenging the additional warming by greenhouse gases under certain obliquity states can permit for widespread seasonally warm conditions which can help to explain the presence of fluvial surface features e g valley networks and hydrous minerals of post noachian age a period when alternate methods do not convincingly explain the sustainability of liquid water furthermore we find that global warming can be achieved with the presence of a darker surface globally which is consistent with both widespread exposure of unweathered basaltic bedrock or the presence of a large surface ocean or sea

vertical profiles of longshore currents and related bed shear stress and bottom roughness the vertical structure of the mean wave driven longshore current over a barred beach is examined on three strong current days during the duck94 experiment and it is found that the bottom boundary layer is well described by a logarithmic profile mean correlation coefficient for all 22 profiles 0 98 the logarithmic profile fits better in the trough where turbulent bottom boundary layer processes predominate than over the bar where breaking wave induced turbulence generated at the surface modifies the profile the surface layer in the presence of waves is well described by adjusting the logarithmic profile for the intermittent presence of water and adding the alongshore component of the mass transport velocity slope of the least squares linear regression between model predictions and observations 1 005 and root mean square rms error of 7 bed shear stresses calculated from logarithmic velocity profiles are equated to a quadratic bottom shear stress formulation the associated bed shear stress coefficients vary by more than an order of magnitude across the surf zone 0 0006 0 012 bottom roughness was measured throughout the nearshore using a sonic altimeter mounted on a moving platform the bed shear stress coefficients are positively correlated with bottom roughness linear correlation coefficient 0 6 a higher linear correlation coefficient 0 8 is obtained by subtracting skin friction from the total bed shear stress

dielectric map of the martian northern hemisphere and the nature of plain filling materials 1 a number of observations suggest that an extended ocean once covered a significant part of the martian northern hemisphere by probing the physical properties of the subsurface to unprecedented depth the marsis mars express provides new geophysical evidences for the former existence of a late hesperian ocean the vastitas borealis formation located inside a putative shoreline of the ancient ocean has a low dielectric constant compared with that of typical volcanic materials we show that the measured value is only consistent with low density sedimentary deposits massive deposits of ground ice or a combination of the two in contrast radar observations indicate a distribution of shallow ground ice in equilibrium with the atmosphere in the south polar region we conclude that the northern plains are filled with remnants of a late hesperian ocean fed by water and sediments from the outflow channels about 3 gy ago

the thermoluminescence carrier in the dhajala chondrite the thermoluminescence tl sensitivities of 58 chondrules separated from the dhajala h3 8 chondrite have been measured in order to investigate the cause of the 105 fold variation in the tl sensitivity of ordinary chondrites the tl sensitivities of the individual chondrites range over nearly two orders of magnitude from 0 002 to 0 12 where 4 mg of bulk dhajala powder 1 with no correlation with chondrule mass cross sectional area or diameter some chondrules have tl per unit mass ten times that of bulk dhajala powder and mass tl balance arguments suggest that these chondrules are a major tl carrier the composition of 15 chondrules was also determined and it was found that high tl chondrules tend to have ca contents at the upper end of the range observed these observations are consistent with the tl sensitivity variation in ordinary chondrites which is related to metamorphism being caused by the devitrification of glass to produce feldspar and with feldspar being the dominant tl phosphor in dhajala that chondrules are an important tl carrier would also be consistent with primary feldspar as the tl phosphor but petrologic observations probably make this appear unlikely

chemical and physical studies of type 3 chondrites viii thermoluminescence and metamorphism in the co chondrites the thermoluminescence properties of nine co chondrites have been measured with the exception of colony and allan hills a77307 alha 77307 whose maximum induced tl emission is at approximately 350 c co chondrites exhibit two tl peaks one at 124 7 c 130 c peak and one at 252 7 c 250 c peak the 130 c peak shows a 100 fold range in tl sensitivity 0 99 0 21 for isna to 0 010 0 004 for colony and correlates with various metamorphism related phenomena such as silicate heterogeneity metal composition and mcsween s metamorphic subtypes the peak at 250 c does not show these correlations and colony excepted varies little throughout the class 0 3 to 0 07 colony 0 018 0 004 mineral separation experiments and a series of annealing experiments on isna suggest that the tl properties for co chondrites reflect the presence of feldspar in two forms 1 a form produced during metamorphism and analogous to the dominant form of feldspar in type 3 ordinary chondrites and 2 a primary metamorphism independent form perhaps associated with the amoeboid inclusions if this interpretation is correct then the co chondrites have not experienced temperatures above the order disorder temperature for feldspar 500 600 c and they cooled more slowly than comparable i e type 3 5 type 3 ordinary chondrites colony and alha 77307 have atypical tl properties including very low tl sensitivity suggesting that phosphors other than feldspar are important they have apparently experienced less metamorphism than the others and may have also been aqueously altered

small scale morphology across the surf zone small scale 5 m horizontal length nearshore morphologic height variations were measured by combining crab surveys with bed elevations acquired with a 1 mhz sonic altimeter mounted on the crab during the october phase of the duck94 experiment bedform plan views were recorded simultaneously using a 500 khz side scan sonar mounted on the crab waves and currents were measured at the same time significant temporal and spatial variations in the small scale morphology were measured in response to changing waves and currents during the 2 weeks examined three cases are examined in detail 1 mild waves and weak longshore currents resulting in wave ripples throughout the study area 2 storm waves with strong longshore currents resulting in lunate and straight crested mega ripples in the trough of the barred beach and 3 narrow band normally incident waves with a strong rip current resulting in a planar bed except in the throat of the rip where mega ripples were measured wavenumber spectra of the bed were generally broad indicating newly formed ripples coexisted with residual ripples from the past to form complex multi scaled ripple patterns

occurrence of megaripples in a ridge and runnel system sapelo island georgia morphology and processes abstract during 20 31 october 1982 we observed the formation of megaripples in en echelon runnel systems 0 2 2 km long and 8 15 m wide on nanny goat and cabretta island beaches sapelo island georgia the runnels contained a complex assemblage of lower flow regime bedforms which were dominated by large sinuous to lunate megaripples with heights of 15 to 50 cm and wave lengths of 4 to 14 m at times smaller megaripples 80 to 100 cm long and 5 to 10 cm high formed on the backs of the large megaripples small linguoid lunate ripples were superimposed on the megaripples the magaripples form in the fine sand 0 125 0 25 mm during rising high tide associated with higher than normal wave energies and northeasterly waves and wind as the tide rises wave generated surges override the ridge and are translated into unidirectional pulsating flow along the runnel to the south on sapelo island thus producing the megaripples as the tide lowers waves no longer override the ridge and small linguoid lunate ripples form on top of the megaripples as water drains from the runnel because our measured velocity values are lower than those required by experimental work to produce megaripples in fine sand they may represent minimum velocities due to averaging pulses over time and distance these large lower flow regime bedforms produce sets of high angle cross laminae oriented along shore within upper flow regime plane beds and should be allowed for during environmental interpretation of nearshore deposits in the rock record

planetary geomorphology some historical analytical perspectives abstract three broad themes from the history of planetary geomorphology provide lessons in regard to the logic valid reasoning processes for the doing of that science the long controversy over the origin of lunar craters which was dominated for three centuries by the volcanic hypothesis provides examples of reasoning on the basis of authority and a priori presumptions percival lowell s controversy with geologists over the nature of linear markings on the surface of mars illustrates the role of tenacity in regard to the beliefs of some individual scientists finally modern controversies over the role of water in shaping the surface of mars illustrate how the a priori method i e belief produced according to reason can seductively cloud the scientific openness to the importance of brute facts that deviate from a prevailing paradigm

evidence for primitive nebular components in chondrules from the chainpur chondrite abstract the least equilibrated ordinary chrondrites contain chondrules which have experienced little change since the time of their formation in the early solar system these chondrules are excellent indicators of the physical and chemical nature of the solar nebula we separated 36 chondrules from the chainpur ll3 4 chondrite and analyzed each for 20 elements and petrographic properties sampling biases were minimized as far as possible chondrules seem to have formed through the melting of random mixtures of grains comprising a limited number of nebular components the identity of these components can be deduced from chondrule compositions the dominant components appear to be 1 a mixture of metal and sulfide with composition similar to whole rock metal and sulfide 2 refractory ir rich metal 3 refractory olivine rich silicates 4 low temperature pyroxene rich silicates and possibly 5 a component containing the more volatile lithophiles most of the textural types of chondrules formed from the same set of precursor components in some cases chondrules having different textures are almost identical in composition a few unusual chondrule types seem to mainly consist of uncommon nebular components possibly indicating different modes of formation etching experiments confirm that chondrule rims are enriched in metal troilite and moderately volatile elements relative to the bulk chondrules however a large fraction of the volatiles remains in the unetched interior

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

formation of gravel pavements during fluvial erosion as an explanation for persistence of ancient cratered terrain on titan and mars abstract in many terrestrial channels the gravel bed is only transported during rare floods threshold channels and rates of erosion are very slow in this paper we explore how coarse debris delivered to channels on mars and titan from erosion may inhibit further erosion once a coarse gravel channel bed develops portions of the equatorial region of titan are fluvially eroded into banded crenulated terrain some of which contains numerous circular structures that are likely highly degraded large impact craters surviving from the late heavy bombardment no mechanism that can chemically or physically break down ice likely the most important component of titans crust has been unambiguously identified this paper examines a scenario in which fluvial erosion on titan has largely involved erosion into an impact generated megaregolith that contains a modest component of gravel sized debris as the megaregolith is eroded coarse gravel gradually accumulates as a lag pavement on channel beds limiting further erosion and creating a dissected but largely inactive or senescent landscape similar development of gravel pavements occur in ancient mountain belts on earth and partially explain the persistence of appreciable relief after hundreds of millions of years likewise coarse gravel beds may have limited the degree to which erosion could modify the heavily cratered terrains on mars particularly if weathering were largely due to physical rather than chemical weathering processes in a relatively cold and or arid environment

estimating nearshore bedform amplitudes with altimeters abstract estimates of the heights of large 0 1 0 4 m heights and 1 10 m horizontal lengths migrating bedforms on a sandy beach made with fixed single point altimeters are similar to heights estimated from profiles across the bedforms made with altimeters mounted on an amphibious vehicle that traversed the surf zone unlike many profiling systems the robust fixed altimeters can measure bedforms in bubbly sediment laden surf zone waters nearly continuously including during storms thus allowing investigation of the relationships between bedform heights and near bottom velocities to be extended to a wide range of wave conditions the fixed altimeter observations of migrating bedforms suggest a sandy surf zone seafloor is not always smooth during energetic conditions with strong mean currents and large wave orbital velocities

viscous relaxation of impact craters on icy planetary surfaces determination of viscosity variation with depth spacecraft images show that the icy galilean satellites have surfaces with very low topographic relief impact craters on ganymede and callisto are anomalously shallow and are characterized by sharp well defined rims and domed floors these morphological characteristics can be explained by viscous relaxation of topography on an icy crust in which the viscosity is uniform or decreases with depth under these conditions large craters relax more rapidly than small craters therefore explaining a possible underabundance of large craters viscous relaxation on an icy crust that is thin compared to the crater diameter or on a thick icy crust in which viscosity increases with depth could not produce this crater morphology and would result in the more rapid relaxation of small craters rather than large craters the results of this study suggest that more detailed analysis of relaxing impact crater morphology may resolve the rate of viscosity decrease with depth and so provide evidence on the interior thermal evolution of icy planetary bodies

thermoluminescence and the shock and reheating history of meteorites iv the induced tl properties of type 4 6 ordinary chondrites abstract the induced thermoluminescence tl properties of 121 equilibrated ordinary chondrites have been measured the samples were 74 h and 47 l chondrites of which 33 h and 32 l were from antarctica the distribution of tl sensitivities for non antarctic l chondrites differs from that of non antarctic h chondrites consistent with a greater proportion of the former class suffering post metamorphic shock data on the effect of laboratory annealing on tl sensitivity and step wise ar release measurements enable the meteorites to be sorted into three shock related temperature groups

hydrology of early mars valley network incision 1 widespread occurrences of valley networks on mars provide geomorphic evidence for an active hydrologic cycle to constrain the climatic conditions capable of forming the valley networks a hydrological model was used to analyze the valley incision depth and volume of eroded valleys because the absolute magnitudes of precipitation runoff and evaporation are uncertain we have used the ratio of these quantities the x ratio to express climatic conditions the spatial distribution and strength of the correlations between 1 the estimated depth and volume of eroded material and 2 estimated flood magnitude and valley gradients were investigated as a function of the assumed x ratio we also conducted an analysis of conditions required to have appreciable discharge in selected valley networks which provided the most definitive constraint on martian paleoclimate the other methods show a relatively weak dependency of incision depths and volumes upon the assumed x ratio the multiple regression analyses indicate that incision depth is strongly influenced by gradient and weakly related to modeled flood discharge the factors determining relative depth of incision depend partly on the type of channel bed however postflow modification of the valley networks by mass wasting cratering aeolian infilling and ice related processes precludes direct determination of bed morphology our hydrological analyses suggest that climatic conditions on early mars were at least as moist as those that occurred in the great basin region of the u s when large lakes were present during the pleistocene in terms of the balance of runoff and lake evaporation

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

performance of a sonar altimeter in the nearshore abstract a 1 mhz sonar altimeter with automatic gain control is shown to provide accurate estimates of the distance between the instrument and the seafloor laboratory experiments indicate that distance estimates degrade slightly when the bottom is rough or sloped and when sediment is suspended in the water column results from field tests both within and seaward of the surf zone show some degradation owing to a combination of suspended sediment and bubbles bed undulations and perhaps the dynamic nature of the sand bottom under waves seaward of the surf zone the bottom can be located within 2 cm nearly continuously whereas inside the surf zone the bottom can be located only intermittently and the accuracy decreases to 3 cm a 300 m long cross shore transect of 16 altimeters was deployed from the shoreline to about 4 m depth for 3 months in summer fall 1994 near duck nc results show that the altimeters are robust and can usually provide estimates of the seafloor position every few minutes even in the surf zone during large storms

megaripple migration in a natural surf zone migrating megaripples are bedforms that appear in the surf zone of sandy coasts1 with heights of 0 1 0 5 m and wavelengths of 1 5 m they are similar in size and shape to small dunes large ripples or sand waves such sedimentary bedforms have been studied in subaerial2 steady flow3 and intertidal4 environments as well as in laboratory flume experiments5 they affect overlying currents by introducing hydraulic roughness4 6 and may provide a mechanism for sediment transport7 8 as well as forming sedimentary structures in preserved facies9 10 the formation orientation and migration of such bedforms is not understood well11 12 dunes for example can be aligned with their crests perpendicular to steady unidirectional winds13 but in more complex wind fields their orientation becomes difficult to predict14 15 16 17 similarly it is not known how sea floor megaripples become aligned and migrate in the complex flows of the surf zone here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents but are aligned so that the sediment transport normal to the bedform crest is maximized17 this may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns

chemical and physical studies of chondrites x cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites abstract the cathodoluminescence cl properties of eight type 3 ordinary chondrites and one l5 chondrite have been determined and phenocryst and mesostasis compositions have been analyzed in the chondrules of four of them semarkona type 3 0 krymka 3 1 allan hills a77214 3 5 and dhajala 3 8 in order to investigate their origins and metamorphic history two major classes of chondrule with eight subdivisions have been identified mainly on the basis of cl properties and 95 of the chondrules can be assigned to these groups on the basis of phenocryst and mesostasis composition class a chondrules consisting of those with plagioclase normative mesostasis with bright cl are subdivided into groups a1 a2 a3 a4 and a5 class b chondrules with little or no cl and having quartz normative mesostases in the least metamorphosed chondrites which becomes feldspathic with metamorphism are subdivided into groups b1 b2 and b3 relationships between the eight chondrule groups can be deduced from their relative abundance in each of the nine chondrites groups a1 a2 b1 and a5 are present in semarkona 15 20 60 5 by number respectively group a5 chondrules in semarkona being more heterogeneous than a5 chondrules in chondrites of higher petrologic type chondrule group a1 evolves into a3 then a4 and then a5 during metamorphism while a2 evolves into a4 and then a5 chondrule group b1 evolves into b2 b3 and then a5 but higher levels of metamorphism are required to complete the series than for the a1 5 series conversion of a group to an adjacent group can be observed in allan hills a77214 3 5 where several chondrules are group b3 in their central regions and group a5 in their outer regions the present chondrule groups are essentially independent of texture since group a and group b chondrules differ in bulk composition redox state and possibly oxygen isotope systematics their relative abundance might be a factor in the creation of the nine chondrite classes

comparative study between rivers in tarim basin in northwest china and evros vallis on mars abstract the morphometric characteristics of the kaidu river and keriya river in the extremely arid tarim basin and the evros vallis on mars were compared to study the formation of the dendritic evros vallis which has great significance for exploring ancient climate of mars the following results were obtained a the average sinuosities of kaidu river keriya river and evros vallis are 1 17 1 35 and 1 32 respectively b the average bifurcation ratios are 3 84 4 73 and 3 43 respectively c the average stream length ratios are 2 21 3 86 and 2 08 respectively d the stream frequencies are 0 017 0 028 and 0 002 respectively e the drainage densities are 0 195 km 1 and 0 217 km 1 and 0 048 km 1 respectively f the stream gradients are 3 74 7 03 and 1 63 respectively g the stream fractal dimensions are 1 70 1 0 and 1 68 respectively paleodischarge estimations at different stream segments of evros vallis support the hypothesis that the v bend area that joints the eastern and western segments possibly has a tectonic origin geomorphological evidence e g tributaries from high resolution images and stream morphometric parameters from a comparative analysis e g concave upward longitudinal profile and stream fractal dimension support previous hypothesis that evros vallis is a mature drainage system formed by precipitation driven surface runoff this drainage process occurred either in a continuously warm wet climate that lasted long enough on early mars or in regional hydrologic cycles consisting of precipitation and occasionally returned runoff in intermittently clement climates

drainage network development in the keanakāko i tephra kīlauea volcano hawai i implications for fluvial erosion and valley network formation on early mars 1 a number of studies have attempted to characterize martian valley and channel networks to date however little attention has been paid to the role of lithology which could influence the rate of incision morphology and hydrology as well as the characteristics of transported materials here we present an analysis of the physical and hydrologic characteristics of drainage networks gullies and channels that have incised the keanak ko i tephra a basaltic pyroclastic deposit that occurs mainly in the summit area of k lauea volcano and in the adjoining ka desert hawai i the keanak ko i tephra is up to 10 m meters thick and largely devoid of vegetation making it a good analog for the martian surface although the scales are different the keanak ko i drainage networks suggest that several typical morphologic characteristics of martian valley networks may be controlled by lithology in combination with ephemeral flood characteristics many gully headwalls and knickpoints within the drainage networks are amphitheater shaped which results from strong over weak stratigraphy beds of fine ash commonly bearing accretionary lapilli pisolites are more resistant to erosion than the interbedded coarser weakly consolidated and friable tephra layers because the banks of the gullies and channels are easily eroded widths vary downslope similar to martian valley networks that have been characterized as degraded the floors of the gullies and channels tend to be low relief with few prominent bed forms reflecting the large proportion of sediment transported as bed load in high energy but short lived flood events we calculate that the average flow velocities within the drainage networks are typically 1 m 24 h given some recent modeling of the early martian climate our observations imply that rainfall on early mars could also be associated with large intense events and that martian valley network formation may be related to similar cyclonic storms

noachian climatic conditions on mars inferred from valley network junction angles abstract valley networks vns on mars offer convincing evidence for its past water activities previous research empirically and theoretically suggested that the geometry properties such as junction angles of streams on earth formed under different climatic conditions are different thus the geometry properties of vns can be used to infer the early mars climatic conditions under which vns were formed the frequency distribution of junction angles is less influenced by the post formational modification processes than valley density and cross section and can be accurately extracted from low resolution data we first analyzed the association between the junction angles and environmental factors on earth the results suggested that the climatic factors are stronger than or on par with the geologic factors in controlling junction angles and that climatic parameters aridity index ai and mean annual precipitation map can be estimated from junction angles we then applied the associations between terrestrial junction angle and climatic conditions to estimate the ai and map of mars considering the different solar radiation of the two planets the spatial analysis of inferred climatic conditions showed that the noachian mars had an active global hydrological cycling and mars was warm during the vns formation period the duration of warm mars is estimated by the ratio between the required water volume to form vns and the runoff discharge derived from map the range of warm period is from 4 4 to 77 million years the results support the hypothesis that mars was episodically warm

hummocky cross stratification and post vortex ripples length scales and hydraulic analysis duke 1987 argues that the structure reported by greenwood sherman 1986 as hummocky cross stratification from a shallow lacustrine environment is instead bedding formed by simple post vortex oscillation ripples his primary concern is with the length scale of the structures identified in box cores however using measured flow data it is shown here that existing models of bedform generation based upon wave orbital velocity orbital diameter and grain diameter do not support a simple post vortex ripple interpretation in particular the relative steepness of the structure refutes such an origin the structural characteristics of the lacustrine cores most closely match those associated with classic hummocky cross stratification and were produced under a combined oscillatory quasi steady flow field

computer generated global map of valley networks on mars 1 the presence of valley networks vn on mars suggests that early mars was warmer and wetter than present however detailed geomorphic analyses of individual networks have not led to a consensus regarding their origin an additional line of evidence can be provided by the global pattern of dissection on mars but the currently available global map of vn compiled from viking images is incomplete and outdated we created an updated map of vn by using a computer algorithm that parses topographic data and recognizes valleys by their morphologic signature this computer generated map was visually inspected and edited to produce the final updated map of vn the new map shows an increase in total vn length by a factor of 2 3 a global map of dissection density d derived from the new vn map shows that the most highly dissected region forms a belt located between the equator and mid southern latitudes the most prominent regions of high values of d are the northern terra cimmeria and the margaritifer terra where d reaches the value of 0 12 km 1 over extended areas the average value of d is 0 062 km 1 only 2 6 times lower than the terrestrial value of d as measured in the same fashion these relatively high values of dissection density over extensive regions of the planet point toward precipitation fed runoff erosion as the primary mechanism of valley formation assuming a warm and wet early mars peculiarity of the global pattern of dissection is interpreted in the terms of climate controlling factors influenced by the topographic dichotomy

martian geomorphology from fractal analysis of drainage networks 1 an alternative approach to conventional planetary terrain analysis is proposed martian terrains represented by topography based on the mars orbiter laser altimetry mola data are represented as a series of drainage basins regardless of the historical presence or absence of actual fluid flow a fractal analysis of each drainage network computationally extracted from an underlying terrain yields a network descriptor a list of four numbers that describes the traits of a network network descriptors are used for a quantitative characterization and classification of martian surfaces we have extracted and analyzed 387 drainage networks from 74 martian locations representing all major epochs and geological units to investigate whether their network descriptors are capable of differentiation between different epochs and geological units we have found that our approach can distinguish morphologically different terrains but only in a statistical sense in particular the method could be used to measure the degree of surface cratering and thus the age of the surface in addition for surfaces that are not heavily cratered the method is capable of distinguishing between different geological units we have found no global trends in the character of martian drainage networks their network descriptors show no systematic dependence on location or elevation our analysis reveals that all noachian surfaces grouped in the npld geological unit have very similar network descriptors regardless of prominence and integration of their visible fluvial features the comparison between statistical description of npld and terrestrial drainage networks shows overall similarities but also some marked differences because of these differences the notion of sustained rainfall on mars during the noachian epoch is inconsistent with our findings but a limited rainfall is compatible with our results