earth and mars water inventories as clues to accretional histories abstract the earth has 2 7 km of water on its surface its mantle contains at least 150 ppm water and probably significantly more depending on the amount of undepleted mantle and subducted crustal water that is present geologic evidence suggests that a few hundred meters of water are close to the martian surface but evidence from snc meteorites indicates that the martian mantle is very dry containing no more than about 35 ppm water part of the difference in water content of the mantles of the two planets is attributed to plate tectonics however the earth s mantle appears to contain at least several times the water content of the martian mantle even accounting for plate tectonics we attribute the difference to two possible causes the first possibility is that melting of the earth s surface during accretion as a result of the development of a steam atmosphere allowed impact devolatized water at the surface to dissolve into the earth s interior in contrast because of mars smaller size and greater distance from the sun the martian surface may not have melted so that the devolatilized water could not dissolve into the surface a second and preferred possibility is that mars like the earth acquired a late volatile rich veneer but it did not get folded into the interior as with the earth but instead remained as a water rich veneer the perception of mars as having a wet surface but a dry interior is consistent with what we know of the geologic history of mars which can be viewed as the progressive intrusion and overplating of a water rich crust by dry mantle derived volcanic rocks

mars water isotope d h history in the strata of the north polar cap inferences about the water cycle abstract a time varying stable isotope model for the d h history of mars water cycle is developed with variable atmosphere space loss rate ground and ice cap flux rates it considers coupled ground reservoirs and traces d h in the air and reservoirs secularly and over obliquity cycles the various flux rates are prescribed time variables that simulate surface flux and solar driven space loss rates predicted bulk averages for the ice cap ground ice reservoirs and atmosphere span the observed ranges reported by mumma et al mumma m j novak r e disanti m a bonev b dello russo n magee sauer k 2003 the martian atmosphere conference reports of sixth international conference on mars atmosphere no 3186 when the dominant obliquity cycle variations are scaled so that the model delivers present seasonal variations the present long term bulk d h average for the ice cap is 2 7 equivalent to 1700 in d wrt smow the obliquity driven d h cycle in the ice cap s layers varies between 3 and 6 the smaller more accessible reservoirs have larger bulk averages with the smallest being able to reach d h values over 9 within 10 5 years small hypothetical solar activity driven variations in the escape rate to space and in the fractionation constant krasnopolsky v a feldman p d 2001 science 294 1914 1917 for the escape process can produce a solar wiggle whose d h amplitude can reach 0 1 d amplitude of 100 because of the temporal variability a single modern measured atmospheric d h ratio at a particular ls cannot tell very much about the total water inventory of mars a bulk average for the northern ice cap and better still a dated vertical profile of d h from the ice cap would however go a long way towards illuminating the modern water history of mars the age and stability of the northern ice cap and the d h history locked in the layering is discussed an ice cap that is very young and exchanges its mass through the atmosphere often will necessarily have a large d h

simultaneous vibroseis recording1 an experiment was undertaken at bp s fulbeck geophysical test site to compare the viability of various simultaneous vibroseis recording techniques which are often recommended as a means of improving data acquisition production rates for 3d seismic surveys of particular interest were a the ability to separate the signals from each source during processing b the generation and suppression of harmonics and c the effects of any source interaction two vibrators were deployed with a baseplate separation of 10 m about a borehole containing a vertical array of geophones our analysis concentrated on the groundforce signals measured at each vibrator and the far field signatures measured using a vertical geo phone at a depth of 204 m by comparing single vibrator records with similar but separated records from a simultaneous recording sequence signal separability harmonic suppression and vibrator interaction could be fully studied separated far field signatures from simultaneous vibroseis methods using combinations of up and downsweeps exhibited unsuppressed harmonics and substantial energy from the undesired source which leaked through the correlation process the up down method was capable of separating the signal from each source by only 12 7 db and is therefore unsuitable as a field technique the variphase simultaneous vibroseis methods studied afforded some harmonic suppression and gave signal separations of about 30 0 db use of variphase simultaneous vibroseis methods will compromise the quality of the data recorded when compared with single source acquisition methods none of the simultaneous vibroseis methods tested provided adequate signal separation and therefore cannot be recommended as data acquisition techniques the alternate sweeping method coupled with multispread recording will give the desired improvement in data acquisition rates while preserving the necessary quality of our seismic data

a rapid decrease of the hydrogen corona of mars mars is believed to have lost much of its surface water 3 5 billion years ago but the amounts that escaped into space and remain frozen in the crust today are not well known hydrogen atoms in the extended martian atmosphere some of which escape the planet s gravity can be imaged through scattered solar uv radiation hubble space telescope hst images of the ultraviolet h ly emission now indicate that the coronal h density steadily decreased by a factor of roughly 40 over 4 weeks a far greater variation than had been expected the leading candidate cause is a decrease in the source rate of water molecules from the lower atmosphere consistent with seasonal changes and a recent global dust storm this implies that the rate of escape of martian hydrogen and thereby water into space is strongly dependent on the lower atmospheric water content and distribution

nonlinear multitrace genetic inversion applied on seismic data across the shtokman field offshore northern russia seismic inversion is an important processing step for characterizing reservoirs with properties predicted away from well controls a new approach to inversion and reservoir modeling is based on a nonlinear multitrace seismic inversion algorithm neural network solutions for the inversion problem exist whereby a multiattribute analysis increases output reliability a more robust 3d working method is proposed that uses a simple nonlinear operator the method is fast user friendly and cost effective initial input is formed by poststack seismic data and relevant well logs e g acoustic impedance the latter serve as a training and control point set to calculate optimized weights in the neural network scheme the nonlinear output operator trans forms the seismic data into the desired log response equivalent crucial is finding a real regional minimum for the difference between the computed synthetic and the recorded seismic traces at the target location intelligent data decimation eliminates the number

c n o isotope fractionation on mars implications for crustal h2o and snc meteorites the viking measurement of15n enrichment on mars has been interpreted as setting low limits on the original complement of volatiles which seems incompatible with estimates around 0 5 3 km depth of crustal h2o a re examination of mechanisms losing nitrogen to space shows that currently operating chemical processes alone give a fractionation ratio for15n 14n of 0 69 0 75 combining this with the diffusive separation gives the ratio of escape rates as 0 53 0 62 if there has been no interchange with the crust this implies under 1 mb initial complement of nitrogen alternatively the low 62 16 enrichment of15n is explicable as resulting from continuous outgassing from the martian surface together with the current loss processes this is supported by the ordinary values of n2 inert gases in snc meteorites and is compatible with a proportionate initial complement of n2 lost via physical or chemical processes early in the planet s evolution persistence to the present epoch of abundant kilometre deep h2o is thus acceptable as diffusive separation and chemical loss processes for oxygen give a fractionation ratio for18o 16o of 0 75 the observed enrichment by 10 suggests interchange with the large reservoir of crustal h2o probably polar ice is dominant 13c 12c fractionation is a little stronger but escape rates two orders of magnitude lower so enrichment by 3 6 implies much less interchange with the surface the martian atmosphere as occluded in snc meteorites during the last 1 3 ga would be a little lighter isotopically in c and o but potentially heavier in n than the current atmosphere

the use of pseudorandom sweeps for vibroseis surveys pseudorandom vibroseis sweeps have long been suggested as an alternative to standard linear sweeps due to their potential for having superior orthogonality a lower likelihood for infrastructure damage and increased low frequency content in the past they were also attractive as they have a better autocorrelation shape although that is less important today their use has been limited but the increasing popularity of simultaneous acquisition techniques has rekindled interest as they offer the ability to reduce interference noise a wide variety of methods for generating pseudorandom sweeps have been developed over the last 45 years this paper gives an overview of the motivations for their use before classifying and describing the different sweep types finally the sweeps will be compared in terms of their major attributes including their suitability for simultaneous surveys

oxygen isotopic composition of carbonate in the nakhla meteorite implications for the hydrosphere and atmosphere of mars abstract we have located small areas of siderite within the mesostasis of the nakhla meteorite high concentrations of mn up to 50 rhodochrosite and elevated d h ratios indicate that the siderite is not a terrestrial alteration product the isotopic composition of oxygen in the siderite has been determined with the manchester isolab 54 ion microprobe the siderite has 18 o 34 1 which is higher than any other martian carbonate yet reported if the 18 o value is the result of equilibration with water at 2 h 2 o produced during the degassing of mars and not modified subsequently isotopically formation from a water rich fluid at 60 c requires that the fluid was heavy isotope enriched relative to fluids produced during planetary degassing an enrichment of 8 15 is consistent with theoretical outgassing models that are able to account for enhancements of 17 o in martian alteration products estimated deposition temperatures would be raised to 80 170 c the effect of a global scale fixation of martian co 2 as carbonate operates in the opposite direction and could lead to a reduction in 18 o of the martian hydrosphere of a few permil

oxygen isotopic record of silicate alteration in the shergotty nakhla chassigny meteorite lafayette samples from a suite of shergotty nakhla chassigny snc meteorites were analyzed for their o isotopic ratios by a modified version of the laser fluorination technique measured isotopic ratios 17o 16o and 18o 16o from bulk samples of the shergottites eeta79001 shergotty and zagami the nakhlite lafayette and chassigny are similar to those reported in the literature as are those from olivine and pyroxene mineral separates from lafayette iddingsite a preterrestrial alteration product of lafayette was measured for the first time as a separate phase oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum 18o of 14 4 for a 90 separate based on these measurements end member iddingsite has a 18o of 15 6 which places it among other 18o enriched secondary phases carbonate and silica observed in snc meteorites the relatively large difference in 18o between iddingsite and the olivine and pyroxene it replaces 11 is typical of low temperature alteration products a range of crustal fluid 18o values can be interpreted from the 18o for end member iddingsite assuming isotopic equilibrium was achieved during low temperature hydrous alteration 100 c treiman et al 1993 the calculated range of values 15 to 5 depends on many factors including 1 the modal mineralogy of iddingsite 2 potential isotopic exchange among other o bearing phases such as host silicate and carbonate and 3 exchange with evolved or exotic o reservoirs on mars despite the lack of constraints the calculated range is consistent with isotopic exchange and possibly equilibria among components of the co2 carbonate iddingsite h2o system at low temperature the snc meteorite samples in this study have 17o values that are indistinguishable from bulk mars 0 30 except for a single small sample of iddingsite that has an anomalous 17o of 1 4 while analytical difficulties make isotopic measurements for this sample problematic the 17o is similar in direction to 17o reported for waters extracted from bulk samples of lafayette karlsson et al 1992 if the 17o for iddingsite is confirmed it can be concluded that evolved or exotic fluids on mars have contributed volatiles to the o reservoir from which iddingsite formed 130 to 700 ma ago

a model for co isotopic signatures of evolving ground ice in the cold dry environments of earth and mars abstract the basics of the model rego are summarized including diffusive water vapor transport ice content adsorption and the isotopic ratios of the various water species inclusion of a temperature and stress strain solution is also described as are the effects of cracking when the tensile breaking strengths are exceeded cracking is viewed as a multi scale phenomena whereby the larger cracks are produced by chaining together smaller ones after some validation the model is applied to the upper university valley antarctic dry valleys data and to the phoenix landing site at lat 69n on mars for the university valley the model when forced by measured diurnal temperature cycles and known relative humidity reproduces some of the complex the ice content and isotope structure found in the upper university valley ground ice cores the model takes a few hundred years to fill the pores just under the ice table the excess ice observed in the university valley cores can be produced by thermal cracking combined with the diurnal temperature cycle time taken to achieve the observed excess ice content is of order 10 4 years there is limited subsurface data for the phoenix site but there are measured ice table depths surface thermal properties and met variables there is enough to do diurnal and seasonal runs of the rego model as with the university valley the upper few tens of centimeters icing are controlled by the diurnal temperatures largely in the warmer part of the year the observed ubiquitous pore full ice right at the ice table could be produced from a dry soil in about 10 3 a and the nearly pure ice patches could be produced by the cracking diffusion mechanism in about million years if shear stresses are included emplacement of ice down to 10 m is possible using the seasonal temperature cycle and cracking excess ice in the upper meter could produced by the model in about 6 10 6 a if the temperature at the phoenix site was 10 20 deg warmer

vertical resolution of thick beds thin beds and thin bed cyclothems resolution has two common definitions the first of these relates to determination of the position of a reflector in time or space resolution by this definition is inversely related to pulse width or sharpness of the wavelet and potentially directly related to bandwidth of the frequency spectrum the second definition of resolution relates to determination of the spacing of close features such as thin beds this type of resolution is determined by the rayleigh criterion which inversely relates resolution to wavelength resolution of thin beds improves with shorter wavelength or higher frequency in comparison to the rayleigh criterion the ricker and widess criteria improve the resolution potential of thin beds but they rely on models of the reflectors and require that the beds be isolated it is a long established and widely accepted axiom that the best wavelets contain bandwidths of at least a couple of octaves this results in wavelets with reduced side lobes and ringiness a more easily interpret

depositional environments and sequence stratigraphy of paralic glacial paraglacial and postglacial upper ordovician siliciclastic deposits in the murzuq basin sw libya abstract the application of sequence stratigraphy methods to glaciogenic deposits is more problematic than in normal paralic deposits because changes in the relative sea level are strongly influenced by an interplay between glacial advance and retreat and concomitant isostatic loading and rebound of the continental shelf the study of outcrop and subsurface sections of the upper ordovician glaciogenic melaz shuqran and the mamuniyat formations murzuq basin sw libya yielded important information on understanding changes in the relative sea level related to glacier movements three depositional sequences were recognized depositional sequence one ds 1 corresponds to the entire melaz shuqran formation that was bounded below by subglacial erosion surface i e sequence boundary sb formed during glacier advance into shallow water areas this surface correlates with a transgressive surface ts in deep water areas and records an initial rise in the relative sea level owing to glacier advance and loading of the continental shelf transgression occurred due to the slower rate of eustatic sea level fall than the isostatic loading the transgressive systems tract tst comprises shoreface sandstones and offshore mudstones diamictites with ice rafted debris further rise in relative sea level was associated with glacial retreat which resulted in sediment starvation in deep water areas and the formation of a condensed section these deposits represent glacial depositional systems the highstand systems tract hst comprises prograding deltaic deposits which was formed when the rate of sediment supply exceeds the rate of relative sea level rise the hst deposits represent paraglacial depositional systems depositional sequence two ds 2 corresponds to the lower and middle part of the mamuniyat formation and is bounded below by deep erosional surface sb that cuts into ds 1 as an incised valley which was formed during glacial advance across the continental shelf incision occurred due to the faster rate of eustatic sea level fall than the rate of isostatic loading glacier retreat and the concomitant rise in relative sea level resulted in the deposition of braided fluvial sediments in a lowstand systems tract lst and tide dominated estuarine sediments in a tst these deposits represent glacial depositional systems the hst sediments represent prograding foreshore to shoreface deposits which were formed when the rate of sediment supply exceeded the rate of relative sea level rise these deposits represent paraglacial depositional systems depositional sequence three ds 3 corresponds to the upper part of the mamuniyat formation and is bounded below by an erosional surface sb that was formed as a result of isostatic rebound associated with relative sea level fall ds 3 lst comprises gilbert type deltaic conglomeratic sandstones grading upwards into sandstones subsequent relative sea level rise during the late ordovician resulted in deposition of shoreface tst sandstone further rise in the relative sea level resulted in sediment starvation in deep water areas and the formation of thin hardground layer i e condensed section that marks the upper boundary of late ordovician deposits this study provides predictive model for the spatial and temporal distribution of ancient glaciogenic depositional facies that may have important implications in hydrocarbon explorations

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

application of amplitude spectrum and genetic inversion to determine shaly facies distribution a case study murzuq basin libya late ordovician glacial deposits of the mamuniyat formation are the main oil reservoir in the murzuq basin in libya autopicking the strong reflection at the base of the silurian shales can be used to map the top of the mamuniyat reservoir in the area where it is in direct contact with the silurian shales however in areas where the bir tlacsin formation a mud prone unit is between the silurian shales and the mamuniyat reservoir the top of the mamuniyat is difficult to pick because the units juxtaposed across the boundary are too similar to produce a strong reflection defining the bir tlacsin facies is important because it impacts hydrocarbon accumulation and migration to predict the distribution of the shaly facies of bir tlacsin and enhance mapping of the top mamuniyat reservoir we utilized a continuous wavelet transform to identify the distinctive thickness of the hot shale and bir tlacsin units we also used genetic inversion to distinguish the bulk density of the bir tlacsin facies a 64 hz frequency gave good time resolution to the amplitude spectrum and was used to predict the facies distribution of the bir tlacsin in contrast the 24 hz frequency showed good frequency resolution of the amplitude spectrum and was used to estimate the temporal thickness of the non reservoir unit of bir tlacsin and hot shale that estimate was then used to modify the autopick horizon for the base of the silurian reflector to approximate the top of the mamuniyat reservoir because of the large density contrast between the shaly facies of the bir tlacsin and the underlying and overlying units inverted density also provides a way to predict the distribution of the bir tlacsin through estimated temporal thickness and to enhance mapping of the top mamuniyat reservoir through mapping the base of the inverted density of the bir tlacsin a comparison between mapping of the top reservoir using spectral decomposition and inverted density with respect to autopick shows that both methods improved the top of the mamuniyat reservoir mapping prediction of the presence of bir tlacsin and improved accuracy of the top of the mamuniyat reservoir mapping reduce the risk of drilling the shaly facies of bir tlacsin and provide a better estimate of the reservoir reserve

geophysical interpretation methods applied at alpine oil field north slope alaska alpine oil field located 34 miles west of kuparuk river field on the north slope of alaska figure 1 and owned by phillips alaska 78 and anadarko petroleum 22 is estimated to contain more than 400 million barrels of proven plus potential oil and 1 billion barrels of oil in place following the discovery well drilled in 1994 the arco bergschrund 1 the field was delineated over two successive winter drilling seasons six wells and four sidetracks were drilled in the delineation phase in 1996 a 3 d seismic survey was acquired to prepare for field development

complex seismic trace analysis of thin beds displays of complex trace attributes can help to define thin beds in seismic sections if the wavelet in a section is zero phase low impedance strata whose thicknesses are of the order of half the peak to peak period of the dominant seismic energy show up as anomalously high amplitude zones on instantaneous amplitude sections these anomalies result from the well known amplitude tuning effect which occurs when reflection coefficients of opposite polarity a half period apart are convolved with a seismic wavelet as the layers thin to a quarter period of the dominant seismic energy thinning is revealed by an anomalous increase in instantaneous frequency this behavior results from the less well known but equally important phenomenon of frequency tuning by beds which thin laterally instantaneous frequency reaches an anomalously high value when bed thickness is about a quarter period and remains high as the bed continues to thin in this paper complex trace analysis is applied to a synthetic model of a we

negative δ18o values in allan hills 84001 carbonate possible evidence for water precipitation on mars the martian meteorite alh84001 contains 1 by weight of carbonate formed by secondary processes on the martian surface or in the shallow subsurface the major form of this carbonate is chemically and isotopically zoned rosettes which have been well documented elsewhere this study concentrates upon carbonate regions 200 m across which possess previously unobserved magnesium rich inner cores interpreted here as rosette fragments surrounded by a later stage cement containing rare ca rich carbonates up to ca81mg07fe04mn07 intimately associated with feldspar high spatial resolution ion probe analyses of ca rich carbonate surrounding rosette fragments have 18ov smow values as low as 10 these values are not compatible with deposition from a global martian atmosphere invoked to explain alh84001 rosettes the range of 18o values are also incompatible with a fluid that has equilibrated with the martian crust at high temperature or from remobilisation of carbonate of rosette isotopic composition at martian atmospheric temperatures the small co2 gas co2 ice fractionation makes meteoric co2 an unlikely source for 10 carbonates in contrast closed system rayleigh fractionation of h2o can generate 18oh2o 30 as observed at high latitudes on earth we suggest that atmospheric transport and precipitation of h2o in a similar fashion to that on earth provides a source of suitably 18o depleted water for generation of carbonate with 18ov smow 10

orthogonal vibroseis sweeps vibroseis is a method that imparts coded seismic energy into the ground the energy is recorded with geophones and then processed using the known coded input signal the resulting time domain representation of vibroseis data is an impulsive wavetrain with wavelet properties consistent with the coded input signal convolved with the earth s reflectivity series historically vibratory seismic surveys collect data from one source location at a time summing one or more sources at each location we present a method of designing orthogonal sweeps using the concept of combisweeps the orthogonal sweeps allow simultaneous recording and later separation of two or more unique source locations orthogonality of sweeps permits separation of the data into unique source location field records by a conventional correlation procedure the separation power of the orthogonal sweeps is demonstrated by a comparison between separated data and data acquired with one vibrator separation noise was at a negligible level for our demonstration data sets when two vibrators were located 50 m to 200 m apart coincident generation and recording of two vibroseis sweeps at different locations would allow almost double the amount of data to be recorded for a given occupation time and requires only half the storage medium

mars volatile evolution implications of the recent measurement of 17o in water from the snc meteorites escape of oxygen to space on mars is capable of producing a fractionation of oxygen isotopes in the remaining oxygen which is off of the fractionation line produced by the usual mass dependent exchange processes the magnitude of fractionation which can occur can be larger than that which was measured in oxygen in water derived from the snc meteorites thought to have come from mars in conjunction with the apparent lack of fractionation of 18o in the atmosphere this result suggests that less than 25 of the oxygen in the martian climate system has been lost over geologic time other mechanisms also might be able to produce such a fractionation so that this conclusion is not unique however it is consistent with other lines of evidence there is no requirement for an initial volatile inventory with an isotopic composition different from that of the bulk planet as might be the case for a late veneer of volatile rich material

muting the noise cone in near surface reflection data an example from southeastern kansas a 300 m near surface seismic reflection profile was collected in southeastern kansas to locate a fault s associated with a recognized stratigraphic offset on either side of a region of unexposed bedrock a substantial increase in the s n ratio of the final stacked section was achieved by muting all data arriving in time after the airwave methods of applying traditional seismic data processing techniques to near surface data 200 ms of data or less often differ notably from hydrocarbon exploration scale processing 3 4 s of data or more the example of noise cone muting used is contrary to normal exploration scale seismic data processing philosophy which is to include all data containing signal the noise cone mute applied to the data removed more than one third of the total data volume some of which contains signal in this case however the severe muting resulted in a higher s n ratio in the final stacked section even though some signal could be identified within the muted data this example supports the suggestion that nontraditional techniques sometimes need to be considered when processing near surface seismic data

utilizing spectral decomposition to determine the distribution of injected co2 at the snohvit field time lapse 3d seismic reflection data covering the co2 storage operation at the snohvit gas field in the barents sea show clear amplitude and time delay differences following injection the nature and extent of these changes suggest that increased pore fluid pressure contributes to the observed seismic response in addition to a saturation effect spectral decomposition using the smoothed pseudo wigner ville distribution has been used to derive discrete frequency reflection amplitudes from around the base of the co2 storage reservoir these are utilized to determine the lateral variation in peak tuning frequency across the seismic anomaly as this provides a direct proxy for the thickness of the causative feature under the assumption that the lateral and vertical extents of the respective saturation and pressure changes following co2 injection will be significantly different discrete spectral amplitudes are used to distinguish between the two effects a clear spatial separation is observed in the distribution of low and high frequency tuning this is used to discriminate between direct fluid substitution of co2 as a thin layer and pressure changes that are distributed across a greater thickness of the storage reservoir the results reveal a striking correlation with findings derived from pressure and saturation discrimination algorithms based on amplitude versus offset analysis

deuteronomy a puzzle of deuterium and oxygen on mars mars is covered by channels that were likely formed by liquid water sometime in its past among the very few available clues to a wetter and warmer ancient climate on mars are the isotopic signatures left by processes that have modified its atmosphere over time in their research commentary yung and kass discuss two sets of results in the same issue krasnopolsky et al have used the hubble space telescope to detect the presence of deuterium in the upper atmosphere of mars and farquhar et al report measurements of the martian meteorite alh84001 showing that the oxygen isotopes in the carbonate are fractionated with respect to silicate minerals the findings suggest the presence of chemical processes operating in mars atmosphere that have yet to be fully understood