apatite fission track thermochronometry from central alberta implications for the thermal history of the western canada sedimentary basin apatite separated from 47 cretaceous and tertiary drill core and surface samples from the foreland basin strata of the western canada sedimentary basin wcsb have been analyzed for their apatite fission track aft age and confined track length distribution thermal histories of the fission track data were then estimated using a constrained random search inversion technique based on the durango apatite annealing model most importantly this technique provides an estimate of the peak postdepositional temperature experienced by each sample with error bounds determined by the precision of the fission track data most apatite samples retain at least some tracks that formed prior to the time of maximum cenozoic burial assumed to be coincident with maximum temperature seven apatite samples were fully annealed during burial during or following the laramide orogeny and provide a minimum age of 42 ma for heating lower cretaceous samples from near the deformation front were fully annealed and attained temperatures of at least 119 138 c during maximum burial in contrast stratigraphically equivalent samples at the northeastern end of the transect near the cold lake heavy oil and tar sand deposits did not exceed 80 c paleogeothermal gradients calculated using bounded estimates of the peak temperatures experienced by the samples together with maximum burial estimates from coal moisture studies range from 20 c km near the deformation front to as high as 60 c km near the cratonic edge of the basin this variation has the same trend as present geothermal gradients which range from 30 c km to 45 c km but indicates a greater contrast at the end of the laramide the results are consistent with the concept of heat transport by basinal scale fluid flow

the effects of topographically controlled thermal tides in the martian upper atmosphere as seen by the mgs accelerometer abstract mars global surveyor accelerometer observations of the martian upper atmosphere revealed large variations in density with longitude during northern hemisphere spring at altitudes of 130 160 km all latitudes and mid afternoon local solar times lsts this zonal structure is due to tides from the surface the zonal structure is stable on timescales of weeks decays with increasing altitude above 130 km and is dominated by wave 3 average amplitude 22 of mean density and wave 2 18 harmonics the phases of these harmonics are constant with both altitude and latitude though their amplitudes change significantly with latitude near the south pole the phase of the wave 2 harmonic changes by 90 with a change of half a martian solar day while the wave 3 phase stays constant suggesting diurnal and semidiurnal behaviour respectively we use a simple application of classical tidal theory to identify the dominant tidal modes and obtain results consistent with those of general circulation models our method is less rigorous but simpler than the general circulation models and hence complements them topography has a strong influence on the zonal structure

propagation of tropospheric gravity waves into the upper atmosphere of mars we study the propagation of gravity waves in the martian atmosphere using a linearized one dimensional full wave model calculations are carried out for atmospheric parameters characteristic of mars orbiter laser altimeter on mars global surveyor mgs observations of apparent gravity waves in high latitude clouds and mgs radio occultation measurements of temperature variations with height suggestive of gravity wave activity waves that reach the thermosphere produce fluctuations in density comparable in amplitude with the density variations detected in mars odyssey aerobraking data gravity waves of modest amplitude are found to deposit momentum and generate significant heating and cooling in the martian atmosphere the largest heating and cooling effects occur in the thermosphere at altitudes between about 130 and 150 km with heating occurring at the lower altitudes and cooling taking place above

mgs radio science electron density profiles interannual variability and implications for the martian neutral atmosphere density of 7 3 8 5 10 4 cm 3 is also measured during solar moderate conditions at mars strong wave number 2 3 oscillations in peak heights are consistently observed as a function of longitude over the 2 martian years these observed ionospheric features are remarkably similar during aphelion conditions 1 martian year apart this year to year repeatability in the thermosphere ionosphere structure is consistent with that observed in multiyear aphelion temperature data of the mars lower atmosphere clancy et al 2000 smith 2004 coupled mars general circulation model mgcm and mars thermospheric general circulation model mtgcm codes are run for mars aphelion conditions yielding mean and longitude variable ionospheric peak heights that reasonably match rs observations a tidal decomposition of mtgcm thermospheric densities shows that observed ionospheric wave number 3 features are linked to a nonmigrating tidal mode with semidiurnal period s 2 and zonal wave number 1 s 1 characteristics the height of this photochemically determined ionospheric peak should be monitored regularly index terms 5435 planetology solid surface planets ionospheres 2459 5409 planetology solid surface planets atmospheres structure and dynamics 6225 planetology solar system objects mars keywords ionosphere mars thermosphere

feldspar diagenesis in the frio formation brazoria county texas gulf coast tremendous quantities of detrital feldspar have been dissolved or albitized below about 14 000 ft 4 267 m in the frio formation oligocene chocolate bayou field brazoria county texas some sandstones no longer contain any unmodified detrital feldspar grains material transfer involved in these reactions is immense affecting at least 15 of the rock volume thus albitization has important implications for several other diagenetic processes that involve feldspars or their components these processes include formation of secondary porosity precipitation of quartz and carbonate cements and the evolution of na ca cl formation water

observations of thermal tides in the middle atmosphere of mars by the spicam instrument 1 we use vertical profiles of martian atmospheric density pressure and temperature from the mars express spicam uv spectrometer to study thermal tides in the poorly studied middle atmosphere region at 70 120 km here we show that nonmigrating tides cause zonal pressure variations of tens of percent and zonal temperature variations on the order of 10 k in these observations wave 2 and wave 3 components are dominant consistent with previous work at lower and higher altitudes and with theoretical predictions normalized pressure amplitudes tend to increase with altitude for the cases and altitudes studied here phases of the pressure variations vary little with altitude indicating long vertical wavelengths for the underlying tidal modes we derive theoretical relationships between zonal variations in temperature and in pressure and find that they are generally satisfied failure of these relationships can be used to infer the presence of multiple tidal modes contributing to a single observed wave component the wave 2 component is dominated by the diurnal kelvin wave 1 dk1 above about 80 km but contains multiple tidal modes below this altitude in one unusual instance 40 s 30 s ls 150 180 and local time of 22 24 h the usually strong wave 2 component is extremely weak the wave 3 component is always dominated by a single tidal mode which for tropical and extratropical latitudes we identify as the diurnal kelvin wave 2 dk2

mars global surveyor and mars odyssey accelerometer observations of the martian upper atmosphere during aerobraking 1 mars global surveyor and mars odyssey accelerometer measurements of martian upper atmospheric densities reveal the large scale and small scale structure of the thermosphere in unprecedented detail meridional density gradients which are seasonally dependent are greater on the dayside than the nightside indicating stronger meridional winds on the dayside density scale heights do not vary greatly with latitude densities and density scale heights are lower on the nightside than on the dayside but the day night contrast is not as great as at venus thus atmospheric circulation plays a greater role in determining the state of the thermosphere on mars than on venus oscillations in density along individual density profiles probably due to gravity waves are common and their amplitudes are tens of percent step like changes in density are also observed but their origin is less clear data coverage is extensive enough to permit studies of weather not just climate

thermotectonic evolution of an extensional dome the cenozoic osogovo lisets core complex kraishte zone western bulgaria the kraishte region of bulgaria is located at the junction of the balkanides and hellenides dinarides tectonic belts fission track analysis on both apatites and zircons documents the cenozoic exhumation of a precambrian basement bounded by low angle detachments late eocene oligocene extension began prior to 47 ma and was dominantly in a top to the southwest direction confirmed by the sense of younging of apatite and zircon ages this crustal extension controlled the formation of half graben sedimentary basins on the hanging walls of the detachments thermal modelling of these hanging wall units provides evidence for heat transfer across the detachments from a relatively warm rising footwall from 32 to 29 ma pervasive magmatic activity resulted in the emplacement of rhyolitic to dacitic subvolcanic bodies and dykes along with intrusion of the osogovo granite the results give evidence for extension in the southern balkan older than and separated from the miocene to quaternary aegean extension this might reflect transtension during northeastward extrusion and rotation of continental fragments around the western boundary of moesia eocene oligocene extension seems to have been controlled by the distribution of earlier thickening all around the carpatho balkanic orocline which is reflected by the cretaceous emplacement of the morava nappe in the kraishte

an interpretation of martian thermospheric waves based on analysis of a general circulation model planetary scale longitudinal variations in density observed by the mars global surveyor accelerometer in the 125 km region can be qualitatively reproduced by the nasa ames mars general circulation model in the 80 km altitude region but only when locations having specific local times are used in the analysis if the model results are averaged over all local times the high altitude longitudinal variations nearly disappear leaving only a small stationary wave 1 pattern consistent with theory and previous modeling studies this analysis suggests that the observed wavelike structures are a result of sampling tidal modes at a limited range of local times rather than by topographically forced rossby waves as previously suggested

post alleghanian unroofing history of the appalachian basin pennsylvania from apatite fission track analysis and thermal models results of apatite fission track analyses on 29 ordovician through permian sandstones from the appalachian basin in pennsylvania are presented ages range from 111 17 to 184 10 ma mean track lengths of 10 71 0 29 to 13 10 0 17 m with unimodal negatively skewed length distributions are indicative of slow cooling the data separate into two groups on an age versus mean length plot the younger group 111 144 ma is found in the structural depressions of the anthracite basin and the broad top basin and adjacent appalachian plateau the older group 144 184 ma is found in the structurally higher southwestern appalachian plateau and juniata culmination and adjacent central plateau fission track data suggest that the basin cooled slowly after the alleghanian orogeny with culminations cooling earlier than depressions cooling histories modeled from apatite fission track data with maximum temperatures constrained by vitrinite reflectance indicate cooling beginning soon after the alleghanian orogeny except in the juniata culmination which apparently experienced synorogenic cooling and unroofing during formation of the underlying duplex model cooling histories and available geologic information indicate that the foreland basin did not experience mesozoic reheating unroofing histories were modeled from fission track cooling histories using heat flow estimates and burial depths derived from vitrinite reflectance profiles the models suggest that the unroofing history of the appalachian basin in pennsylvania can be divided into three episodes an initial episode of relatively rapid cooling and unroofing late permian early jurassic is attributed to flexural rebound of the foreland in response to erosional removal of alleghanian topographic load initial unroofing rates are higher in eastern pennsylvania than in the west consistent with a flexural model an episode of little to no unroofing middle jurassic late oligocene began contemporaneously with the inception of drift at the atlantic continental margin at this time unloading of the orogen was replaced by subsidence and sedimentation on the new margin without flexural rebound the driving force for unroofing of the basin was removed and unroofing slowed greatly an episode of rapid unroofing over the full width of the basin occurred from the miocene to the present although the driving mechanism for unroofing at this time has not been identified it is consistent with increased sedimentation rates in the middle atlantic offshore basins for the same period

fission track and fault kinematics analyses for new insight into the late cenozoic tectonic regime changes in west central sulawesi indonesia abstract the left lateral strike slip central sulawesi fault system csfs composed of the nnw palu koro pkf and the ese matano faults is located within the eastern indonesian triple junction between the pacific indo australian and eurasian plates fault kinematic and fission track analyses show that the late cenozoic central sulawesi deformation results from three successive tectonic regimes 1 a late miocene early pliocene 5 ma wnw trending shortening characterized by transpressional deformation along the pkf and compressional in the poso area this tectonics resulted from the collision between the banggai sula block with sulawesi it produced locally a transpressional regime as a consequence of the northward extrusion of the central sulawesi block limited by the pkf 2 a pliocene collapse tectonic regime associated with w trending extension coeval with these events regional cooling and exhumation took place 3 a quaternary transtensional regime resulting from the combined effects of the central sulawesi block northward motion and extension related to back arc spreading behind the north sulawesi subduction tomini gulf

apatite fission track analysis of oligocene strata in south texas u s a testing annealing models analysis of apatite fission track data from forty seven surface and subsurface samples of fine grained sandstone to pebbly conglomerate from the oligocene catahoula gueydan frio and vicksburg formations documents the response of fission track ages and track length distributions to simple post depositional thermal histories characterized by monotonic heating data from outcrop samples document that the apatite component was derived from source areas characterized by rapid cooling through the temperature range from 120 to 50 c during the early tertiary the apatite population is characterized by a log normal chlorine distribution mean 0 3 wt 0 3 wt consisting predominantly of low cl apatites 80 is 0 5 wt mean track lengths from core samples decrease systematically with increasing depth and temperature the decrease in apatite fission track ages with increasing depth and temperature is less systematic due to the scatter in inherited ages at the time of deposition no tracks were observed in apatite from samples at temperatures above 130 c mean track lengths for the south texas data agree well with those for a similar data set from the otway basin southeastern australia for present day temperatures of 70 c at higher temperatures mean lengths are 1 to 9 m longer than those observed from the otway basin this discrepancy is interpreted to reflect up to 40 ma longer residence times at maximum burial temperatures for the otway basin samples standard deviations about mean lengths are also lower than observed in the otway basin study consistent with the wider variation of cl contents mean 0 8 wt 0 7 wt that characterize apatite from the otway basin recently published apatite fission track annealing models predict significantly different mean track length vs present day temperature profiles for thermal histories believed to be representative of those experienced by sampled south texas strata because of the large uncertainties attributed to present day temperatures 10 c the predicted mean length vs temperature trends for these models essentially fall within or on the uncertainty envelope for the observed trend residuals of predicted minus observed mean lengths suggest that the previously published carlson composite parameter model using an initial mean length of 15 8 m instead of 16 5 m or the crowley et al model for track length reduction down to 11 m provide the best estimates of mean track length reduction over geologic time scales for near end member f apatite populations

evidence for vertical movement of fluids gulf coast sedimentary basin sediments between 10 and 15 km thick have prograded approximately 400 km into the small oceanic basin which formed along the southern margin of north america subsequent to early mesozoic rifting redistribution of mass during burial diagenesis and the chemistry of present day formation waters in jurassic through pleistocene formations document local kilometer scale and in cases basin scale vertical fluid transport within the sedimentary wedge fluid flow is in part driven by porosity reduction which takes place by both physical and chemical processes during burial vertical and horizontal transport also occurs as the result of thermally and salinity generated buoyancy effects input of fluids into the sedimentary wedge from the underlying crust is predicted but not documented

problem of secondary porosity frio formation oligocene texas gulf coast secondary porosity formed by the dissolution of both carbonate and silicate minerals especially k feldspars is widely developed in sandstones of the frio formation oligocene in the texas gulf coast co 2 produced by decarboxylation of organic matter is commonly suggested as the acid required for dissolution material balance calculations indicate that co 2 produced by decarboxylation of organic matter in frio formation shales can account for a regional average of only 1 or 2 secondary porosity in frio formation sandstones yet point count data indicate an average of 10 secondary porosity long distance fluid transport many kilometres and or other mechanisms of acid generation should therefore be considered carbon isotopic data on dissolved inorganic carbon in formation water co 2 in produced natural gas and carbonate cements indicate that co 2 produced by decarboxylation had a minor impact on these carbon reservoirs the reaction kerogen water methane carbon dioxide can explain the isotopic data but alone it is insufficient to account for all the secondary porosity unless long distance material transport is involved

an insight into the breakup of gondwana identifying events through low temperature thermochronology from the basement rocks of madagascar 1 fission track analysis was applied to the precambrian suites of madagascar in order to identify the lower temperature cooling histories and their relationships to the phanerozoic events that affected the island apatite ages range from 431 to 68 ma and zircon ages range from 452 to 238 ma thermochronologically the island can be divided into a southern central and northern region each with a subdivision on an east west basis the southern region is sharply separated from the central region by strongly contrasting apparent apatite ages over the northwest southeast striking ranotsara shear zone rsz the change in apparent ages over the rsz is indicative of later reactivation along younger brittle faults the central region has the oldest ages of the island and has a diffuse contact to the third region northward along the entire western margin of the precambrian basement initial paleozoic exhumation was followed by heating burial by sediments during jurassic and cretaceous times a decrease in ages along the eastern margin from 119 to 68 ma coincides with the predicted positions of the marion hot spot after effects of erosion are considered on the other hand these ages may represent progressive opening of the margin in a southward direction together with associated denudation of the rift shoulder the eastern part of the central region has remained very stable since at least devonian times undergoing only long term very slow exhumation at rates of 1 5 m myr

genetic stratigraphic sequences in basin analysis ii application to northwest gulf of mexico cenozoic basin the northwest gulf of mexico cenozoic sedimentary wedge illustrates the application of genetic stratigraphic sequence analysis and documents several general conclusions 1 sequences defined by regional marine flooding are the principal genetic stratigraphic units of the basin fill continental margins are characterized by repetitive episodes of basin margin offlap punctuated by periods of transgression and marine flooding of the depositional platform 2 continental margin outbuilding is concentrated at one or more shelf edge deltaic depocenters separated by interdeltaic bights depocenters remain fixed during a depositional episode but commonly relocate during transgression and flooding 3 a distinct syndepositional structural style in prograding continental margins results in sporadic uplift of a basin fringing peripheral bulge and accentuates preservation of shelf margin facies along zones of extensional normal faulting and enhanced subsidence 4 genetic stratigraphic sequences commonly reflect an evolving interplay among two or even three variables for example early cenozoic gulf sequences are most closely related to tectonic events of the intraplate source terrane which in turn affect rate and location of sediment supply and basin margin response to loading late cenozoic sequences more closely reflect proposed eustatic cycles

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

numerical assessment of dissolution versus replacement in the subsurface destruction of detrital feldspars oligocene frio formation south texas abstract dissolution is the main process responsible for modifying detrital feldspar assemblages in the oligocene frio formation of south texas accounting for up to 80 of feldspar modification in completely altered assemblages this finding is supported through two independent calculations one based on an estimate of initial feldspar content of the sandstones the other on estimated initial composition of the feldspars themselves volumetric loss of detrital feldspar on the observed scale over such a short time span has major implications for provenance interpretations and for understanding the basin wide mass balance of several major diagenetic components the wide variation of feldspar content and composition at any given depth temperature attests to the premier significance of fluid co position and flux in driving the reactions that bring about dissolution of feldspars in these rocks

late oligocene neogene evolution of europe adria collision new structural and geochronological evidence from the giudicarie fault system italian eastern alps the giudicarie fault system giudicarie sensu stricto meran mauls passeier thurnstein and jaufen faults represents a sharp break in the generally e w strike direction of the orogen scale periadriatic fault system and is a key element for understanding the late oligocene neogene evolution of the alpine chain the kinematics timing and magnitude of movements on the giudicarie fault system are presented here on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples two main tectonic phases are established 1 back thrusting of the austroalpine units over the southern alps around 32 ma recorded by basement and limestone mylonites along the giudicarie and meran mauls faults with transport directions toward 100 110 and 2 later sinistral transpressive displacement characterized by structures at the ductile brittle transition which overprinted the top to e ese thrust related mylonites but also partitioned into a major system of transcurrent faults in the southalpine domain it was during this later event that the periadriatic fault attained its present day geometry however the amount of sinistral displacement along the giudicarie system was only 15 20 km the magnitude is established here from the 15 km sinistral offset of the jaufen mylonites across the passeier brittle fault and the 20 km long gap in the otherwise continuous distribution of oligocene tonalitic lamellae along the giudicarie fault a direct structural connection is also established between the brenner and the jaufen faults this constrains the timing of the second phase since it must postdate the main exhumation phase of the tauern window at 20 18 ma the results of this study argue against an originally straight periadriatic fault the giudicarie fault formed a restraining bend in this part of the periadriatic fault system since at least the late miocene and probably since the late oligocene

cenozoic granitoids in the dinarides of southern serbia age of intrusion isotope geochemistry exhumation history and significance for the geodynamic evolution of the balkan peninsula two age groups were determined for the cenozoic granitoids in the dinarides of southern serbia by high precision single grain u pb dating of thermally annealed and chemically abraded zircons 1 oligocene ages kopaonik drenje eljin ranging from 31 7 to 30 6 ma 2 miocene ages golija and polumir at 20 58 20 17 and 18 06 17 74 ma respectively apatite fission track central ages modelling combined with zircon central ages and additionally local structural observations constrain the subsequent exhumation history of the magmatic rocks they indicate rapid cooling from above 300 c to ca 80 c between 16 and 10 ma for both age groups induced by extensional exhumation of the plutons located in the footwall of core complexes hence miocene magmatism and core complex formation not only affected the pannonian basin but also a part of the mountainous areas of the internal dinarides based on an extensive set of existing age data combined with our own analyses we propose a geodynamical model for the balkan peninsula the late eocene to oligocene magmatism which affects the adria derived lower plate units of the internal dinarides was caused by delamination of the adriatic mantle from the overlying crust associated with post collisional convergence that propagated outward into the external dinarides miocene magmatism on the other hand is associated with core complex formation along the southern margin of the pannonian basin probably associated with the w directed subduction of the european lithosphere beneath the carpathians and interfering with ongoing dinaridic hellenic back arc extension

solar wind interaction with the ionosphere atmosphere and crustal magnetic fields at mars mars global surveyor magnetometer electron reflectometer radio science and accelerometer data 1 the solar wind sw mainly interacts with the martian ionosphere atmosphere however the intense crustal magnetization creates localized minimagnetospheres above the surface the interplanetary magnetic field imf can reconnect with these crustal fields and this allows sw and more energetic particles to precipitate into and heat the neutral atmosphere in localized regions especially in the southern hemisphere a study of 907 electron density profiles obtained by the mgs radio science rs experiment at latitudes from 63 to 77 and 219 profiles at latitudes 69 to 64 5 has been conducted the role of the magnetic field as a driving force of the cross terminator convection is discussed longitudinal variations of neutral atmosphere scale height hpeak derived from the mgs rs data have been analyzed ionospheric parameters are found to be more variable in the southern than in the northern hemisphere this correlates well with the variability of the magnetic field direction from local zenith the scale height of neutral atmosphere density hacc derived from the mgs accelerometer data is also found to be more variable in the southern than in the northern hemisphere

mean and gravity wave structures and variability in the mars upper atmosphere inferred from mars global surveyor and mars odyssey aerobraking densities 1 we have used density measurements obtained during aerobraking ab on mars global surveyor and mars odyssey to examine mean densities and the characteristics and variability of gravity waves gws in the upper atmosphere of mars mean densities exhibit variability with latitude and season and in response to variable forcing and filtering from below these data also reveal significant variability of gws both spatially and temporally in general gw amplitudes increase while apparent horizontal scales remain the same with increasing altitude the dominant spatial scales at the lower ab altitudes are typically 20 200 km and density fluctuations vary from 5 to 50 though even larger values are occasionally observed gw amplitudes also vary significantly with season being generally larger in winter and at middle and high latitudes and apparently reflecting mean source and filtering conditions amplitudes also appear to vary with longitude and time and may provide clues to variability of and interactions with larger scale motions

evidence for nonmigrating thermal tides in the mars upper atmosphere from the mars global surveyor accelerometer experiment 1 mars global surveyor accelerometer experiment density measurements indicate the presence of planetary scale wave structure in the mars upper atmosphere 130 km in particular phase 2 aerobraking observations reveal large amplitude zonal wave 2 and 3 variations in dayside density between 60 latitude these spatial variations in a fixed local solar time reference can be qualitatively reproduced by a mars general circulation model and are identified as a manifestation of eastward propagating nonmigrating thermal tides with long vertical wavelengths the simulated wave 2 variation is dominated by a diurnal period wave 1 kelvin mode while the principal components of the simulated zonal wave 3 structure are a diurnal period wave 2 kelvin mode and a wave 1 semidiurnal tide the characterization of these waves is important for understanding the structure and variability of the martian atmosphere at aerobraking altitudes

the structure of the upper atmosphere of mars in situ accelerometer measurements from mars global surveyor the mars global surveyor mgs z axis accelerometer has obtained over 200 vertical structures of thermospheric density temperature and pressure ranging from 110 to 170 kilometers compared to only three previous such vertical structures in november 1997 a regional dust storm in the southern hemisphere triggered an unexpectedly large thermospheric response at mid northern latitudes increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm throughout the mgs mission thermospheric density bulges have been detected on opposite sides of the planet near 90 degreese and 90 degreesw in the vicinity of maximum terrain heights this wave 2 pattern may be caused by topographically forced planetary waves propagating up from the lower atmosphere

a multiannual record of gravity wave activity in mars s lower atmosphere from on planet observations by the mars climate sounder abstract gravity waves in mars s atmosphere strongly affect the general circulation as well as middle atmospheric cloud formation but the climatology and sources of gravity waves in the lower atmosphere remain poorly understood at earth the statistical variance in satellite observations of thermal emission above the instrumental noise floor has been used to enable measurement of gravity wave activity at a global scale here is presented an analysis of variance in calibrated radiance at 15 4 m 635 665 cm 1 from off nadir and nadir observations by the mars climate sounder mcs on board mars reconnaissance orbiter mro a major expansion in the observational data available for validating models of martian gravity wave activity these observations are sensitive to gravity waves at 20 30 km altitude with wavelength properties h 10 100 km z 5 km that make them likely to affect the dynamics of the middle and upper atmosphere we find that 1 strong moderately intermittent gravity wave activity is scattered over the tropical volcanoes and throughout the middle to high latitudes of both hemispheres during fall and winter 2 gravity wave activity noticeably departs from climatology during regional and global dust storms and 3 strong intermittent variance is observed at night in parts of the southern tropics during its fall winter but frequent co 2 ice clouds prevents unambiguous attribution to gw activity the spatial distribution of wave activity is consistent with topographic sources being dominant but contributions from boundary layer convection and other convective processes are possible

physical characteristics and occurrence rates of meteoric plasma layers detected in the martian ionosphere by the mars global surveyor radio science experiment 1 low altitude plasma layers are present in 71 of 5600 electron density profiles from the martian ionosphere obtained by the mars global surveyor radio science experiment these layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms the mean altitude of the meteoric layer is 91 7 4 8 km the mean peak electron density in the meteoric layer is 1 33 0 25 1010 m 3 the mean width of the meteoric layer is 10 3 5 2 km the occurrence rate of meteoric layers varies with season solar zenith angle and latitude seasonal variations in occurrence rate are particularly strong often exceeding an order of magnitude meteoric layer altitude peak electron density and width are all positively correlated with correlation coefficients of 0 3 0 4 other correlation coefficients between the physical characteristics of meteoric layers and atmospheric or observational properties such as scale height solar zenith angle and solar flux have absolute values that are significantly smaller indicating lack of correlation the photochemical lifetime of plasma in meteoric layers is 12 days and depends on altitude

mars reconnaissance orbiter radio science gravity investigation 1 the objectives of the mars reconnaissance orbiter mro radio science gravity investigation are to improve knowledge of the static structure and characterize the temporal variability of the martian gravitational field relevant to the planet s internal dynamics the structure and dynamics of the atmosphere and the orbital evolution of spacecraft at mars the investigation will utilize range rate and range measurements from x band and when available ka band tracking systems of the mro spacecraft mro will enable a considerable improvement in the spatial resolution and quality of mars global gravity field the low orbital periapsis of mro 255 km will yield gravity maps suitable for study of regional 102 km structure of the crust and lithosphere the addition of tracking data from the mars global surveyor and mars odyssey spacecraft also currently orbiting mars will be useful in decorrelating errors in spherical harmonic coefficients of the gravity field that will improve the quality of the static field studies of the low degree gravity field combined with measurements of rotational dynamics will permit insight about the structure of mars deep interior changes in the low degree spherical harmonic coefficients of the martian gravity field and in polar mass anomalies will be used to track the seasonal cycle of co2 exchange with the surface measurements of spacecraft drag will be used to estimate density variations in the atmosphere relevant to weather patterns and aerobraking of future spacecraft tracking observations will also be used to improve the ephemeris of mars and the masses of the martian moons

provenance of the gueydan formation south texas implications for the late oligocene early miocene tectonic evolution of the trans pecos volcanic field coarse fluvial deposits of the soledad member of the gueydan formation were derived from the trans pecos volcanic field tpvf but the proportions of clast types in the deposits do not match present outcrop abundances in the tpvf basalt and mafic trachyte are most abundant in soledad conglomerate and sandstone durable trachyte forming the largest clasts in contrast the surviving remnant of the tpvf is dominated by silicic lava and tuff the basaltic and trachytic clasts most closely resemble rocks within some of the younger 32 27 ma units in the davis chinati and bofecillos mountains of the tpvf our data suggest that these and similar units were much more widespread at the time of gueydan deposition and were largely stripped from the tpvf during erosion 1 2 km gueydan deposition may have been associated with regional uplift of the tpvf accompanying the onset of basin and range extension this uplift would have provided the steep gradient necessary to transport coarse detritus from the tpvf to the gulf coast basin and range extension eventually disrupted the course of the ancestral rio grande rio conchos thereby cutting off the supply of volcanic detritus and ending gueydan deposition

continuous monitoring of nightside upper thermospheric mass densities in the martian southern hemisphere over 4 martian years using electron reflectometry details are presented of an improved technique to use atmospheric absorption of magnetically reflecting solar wind electrons to constrain neutral mass densities in the nightside martian upper thermosphere the helical motion of electrons on converging magnetic field lines through an extended neutral atmosphere is modeled to enable prediction of loss cone pitch angle distributions measured by the magnetometer electron reflectometer mag er experiment on mars global surveyor at 400 km altitude over the small fraction of mars southern hemisphere 2 5 where the permanent crustal magnetic fields are both open to the solar wind and sufficiently strong as to dominate the variable induced martian magnetotail field spherical harmonic expansions of the crustal fields are used to prescribe the magnetic field along the electron s path allowing least squares fitting of measured loss cones in order to solve for parameters describing the vertical neutral atmospheric mass density profile from 160 to 230 km results are presented of mass densities in the southern hemisphere at 2 a m lst at the mean altitude of greatest sensitivity 180 km continuously over four martian years seasonal variability in densities is largely explained by orbital and latitudinal changes in dayside insolation that impacts the nightside through the resulting thermospheric circulation however the physical processes behind repeatable rapid late autumnal cooling at mid latitudes and near aphelion warming at equatorial latitudes is not fully clear southern winter polar warming is generally weak or nonexistent over several mars years in basic agreement with mgs and mro accelerometer observations the puzzling response of mid latitude densities from 160 to 200 e to the 2001 global dust storm suggests unanticipated localized nightside upper thermospheric lateral and vertical circulation patterns may accompany such storms the downturn of the 11 year cycle of solar euv flux is likely responsible for lower aphelion densities in 2004 and 2006 mars years 27 and 28

dayside ionosphere of mars empirical model based on data from the marsis instrument 1 we present results of a systematic study of electron densities in the dayside martian ionosphere measured by the mars advanced radar for subsurface and ionosphere sounding marsis instrument on board the mars express spacecraft there are two distinct regions controlled by different physical mechanisms the first region is located at altitudes up to about 5 neutral scale heights above the altitude of peak electron density electron densities in this region are well described by the basic chapman theory the observed small deviations can be most probably explained by the neutral scale height and electron temperature increasing with altitude rather than being constant the second region is located at altitudes higher than about 10 neutral scale heights above the altitude of peak electron density it is controlled primarily by diffusion and the observed electron densities decrease exponentially with increasing altitude the corresponding diffusion scale height increases with increasing solar zenith angle which can be probably explained by nearly horizontal magnetic fields in the ionosphere induced by interaction with the solar wind the obtained dependencies can be used as a simple empirical model of the dayside martian ionosphere

mars global surveyor radio science electron density profiles neutral atmosphere implications the mars global surveyor mgs radio sci ence rs experiment permits retrieval of electron density prof iles versus height 90 200 km from occultation mea surements an initial set of electron profiles is examined spanning high northern latitudes early morning solar local times and high solar zenith angles 78 to 81 near aphelion sampling for these 32 profiles is well distributed over longi tude the height of the photochemically driven ionospheric peak is observed to respond to the background neutral den sity structure with a mean height during this season at this location of 134 4 km strong wave 3 oscillations about this mean are clearly observed as a function of longitude and correspond to neutral density variations measured by the mgs accelerometer acc experiment the wave 3 tidal pattern implicated by both the rs and acc datasets is consistent with a semi diurnal wave frequency clearly the height of the martian dayside ionospheric peak is a sensitive indicator of the state of the underlying mars atmosphere this ionospheric peak height can be used as a proxy of the longitude specific non migrating tidal variations present in the mars lower thermosphere

nonmigrating tides inferred from the mars odyssey and mars global surveyor aerobraking data 1 we analyzed mars odyssey ody and mars global surveyor mgs accelerometer density retrievals in narrow local time lt bands during their respective aerobraking phases to study the large scale longitudinal density variations in the martian upper atmosphere the ody data and three seasons of mgs data fall winter and spring all displayed large zonal variations in density especially wave 2 and 3 with little vertical phase variation consistent with previous studies using mgs aerobraking data the large scale density structures were most likely nonmigrating tides sampled at specific lts the wave 2 modes observed in the ody and mgs data were approximately out of phase and their respective lt samplings were approximately 12 hours apart this reinforces the conclusion from previous studies that this mode is most likely an eastward propagating diurnal kelvin wave of zonal wave 1 which is produced by the interaction of the diurnal thermal forcing and the wave 2 component of the martian topography we also note a close association of enhanced gravity wave variances with the strong longitudinal variations in the large scale densities suggesting the possibility of tidal filtering of the gravity wave gw field

resolution of the age structure of the detrital zircon populations of two lower cretaceous sandstones from the weald of england by fission track dating modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography a computer program has been written and used to identify modes in the zircon fission track age distribution within two lower cretaceous sandstone samples from the weald of southern england pronounced modes appear in one rock around 119 ma 160 ma 243 ma and 309 ma and in the other around 141 ma 175 ma 257 to 277 ma and 394 to 453 ma the geological implications of these quite dissimilar zircon age spectra are discussed it is concluded that they support the palaeogeographical models of allen 1981 and indicate that the provenance of the first sample from the top ashdown sandstone member at dallington in east sussex was almost entirely southerly while that of the second from the netherside sand member at northchapel in west sussex was more varied but predominantly westerly and northerly

results of the mars pathfinder atmospheric structure investigation we report on a thorough analysis of the mars pathfinder atmospheric structure investigation asi accelerometer data spanning the altitude range 161 8 9 km entry descent and landing occurred within 850 km of the viking 1 lander and somewhat later in northern summer the early morning entry 0300 hours provided the first opportunity to study mars nighttime atmospheric structure the close proximity to the viking 1 site has permitted a search for changes in atmospheric structure during the 21 years between the landings our results confirm and refine the major features of the atmospheric structure discovered in the initial analysis of the asi results reported by schofield et al 1997 the current analysis has yielded a much better definition of the temperature structure above 90 km altitude pathfinder measured a thermospheric peak temperature of 153 k at 134 km which is 30 k colder than the value found by viking 1 between 110 and 88 km pathfinder found a broad nearly isothermal plateau at 127 k which correlates very well with a similar structure evident in viking 1 data at the same pressures although the pathfinder layer is 25 k colder at levels above 88 km wavelike oscillations with a wavelength 5 km and amplitudes of 2 3 k are evident possibly reflecting gravity or planetary wave activity between 90 and 60 km the average temperature is 20 30 k cooler than viking 1 values large amplitude 10 20 k long wavelength 20 40 km oscillations which show a remarkable correspondence to equivalent structures found in the viking 1 profile at the same pressures occur in this region and are likely due to a diurnal tidal mode between 85 and 77 km a minimum of one oscillation results in temperatures up to 7 k below the saturation temperature of co2 well outside the uncertainties in the measurements and the vapor pressure curve and comparable to observed supersaturations of water in earth s mesosphere between 55 and 16 km temperatures are close to or warmer than viking 1 values superposed long wavelength oscillations correspond well with similar structures observed by viking 1 between 16 and 9 9 km the temperature profile shows an unexpected strong thermal inversion which may reflect radiative cooling due to a water cloud at the base of the inversion temperatures begin to increase abruptly until the last measurement at 8 9 km the viking like temperatures in the lower atmosphere are consistent with the viking like dust optical depths observed by the mars pathfinder imager the cool temperatures in the middle and upper atmosphere may be indicative of significant nighttime cooling at these levels although other interpretations are possible

mars ionosphere a review of experimental results and modeling studies 1 in this paper we review results from atmospheric and ionospheric experiments on the early planetary missions like the mariners mars and viking 1 and 2 orbiters landers we then discuss the new results obtained from the two latest missions namely the mars global surveyor mgs and mars express mex the mgs had three ionospheric and atmospheric related experiments namely 1 the radio science experiment which generated 5600 electron density profiles covering a major portion of sunspot cycle 23 2 the magnetometer electron reflectometer experiment which very clearly answered the question about the presence or absence of martian intrinsic magnetic field and 3 the accelerometer experiment which provided a large database of atmospheric density at various martian locations during the aerobraking phases the topside sounder on the mex provided electron density profiles for altitudes above the primary ionospheric peak with a very high time resolution thereby providing opportunity for exploring ionospheric conditions during events of rapid changes like solar flares unlike venus where simultaneous electron density ion density and magnetic field measurements were made mars lacks this kind of information consequently most of our current understanding of mars plasma environment is based on theoretical models we therefore review the various atmospheric and ionospheric models for mars which have been generated during the last 4 decades

effect of crustal magnetic fields on the near terminator ionosphere at mars comparison of in situ magnetic field measurements with the data of radio science experiments on board mars global surveyor 1 electron density profiles of the ionosphere of mars derived from radio occultation data obtained by the radio science mars global surveyor mgs experiment have been compared with the crustal magnetic fields measured by the mgs magnetometer electron reflectometer mag er experiment in the northern hemisphere the crustal fields are rather weak and usually do not prevent direct interaction between the solar wind sw and the martian ionosphere atmosphere exceptions do occur in the isolated mini magnetospheres formed by the crustal anomalies much stronger crustal fields are located in limited regions in the southern hemisphere and lead to the formation of large scale mini magnetospheres a study of the electron density profiles obtained when the mini magnetosphere regions are near the terminator has been conducted using the magnetic field measurements at altitudes 170 180 km and 400 km the magnitude of the electron density peak and the effective scale height of the electron density for two altitude ranges 145 165 km and 165 185 km have been derived for each of the 326 selected profiles studied in each hemisphere the longitudinal variations of these derived parameters have been studied a significant difference between the large scale mini magnetospheres and regions outside of them has been found the neutral atmosphere is cooler inside the large scale mini magnetospheres the variations of the magnitude of the electron density peak indicate that the electrons are usually hotter inside a large scale mini magnetosphere than outside it appears that the mini magnetospheres formed by strong crustal magnetic fields prevent additional heating of the neutral atmosphere due to direct interaction of the sw and also confine the hotter electrons created by photo ionization

denudation along the atlantic passive margin new insights from apatite fission track analysis on the western coast of south africa apatite fission track aft data from two traverses across the great escarpment of the western coast of south africa are used to reconstruct the tectonic evolution and denudation history of this sector of the atlantic passive margin fission track ages range between 180 and 86 ma modelling of this data identifies two distinct cooling events the first event between 160 and 138 ma is recorded only by the rocks above the escarpment in the karoo area and is tentatively linked to post karoo magmatism 180 ma thermal relaxation the second between 115 and 90 ma results instead from a tectonically induced denudation episode responsible for the removal of up to 2 5 km of crust across the coastal zone in front of the escarpment and less than 1 km on the elevated interior plateau based on these results it is suggested that the cretaceous is the time when most of the elevated topography of southern africa was generated with only a minor cenozoic contribution

upper atmosphere of mars up to 120 km mars global surveyor accelerometer data analysis with the lmd general circulation model 1 mars global surveyor mgs aerobraking accelerometer density measurements are analyzed with the use of the general circulation model gcm at the laboratoire de meteorologie dynamique lmd mgs constant altitude density data are used obtaining longitudinal wavelike structures at fixed local times which appear to be dominated by low zonal wave number harmonics comparisons with simulated data for different seasons and latitudinal bands at constant altitude are performed excellent agreement is obtained between the simulated and observational data for low latitudes with accuracy in both mean and zonal structure higher latitudes show a reduction in agreement between gcm results and mgs data comparisons that result in good agreement with the observational data allow for the study of wave composition in the mgs data in particular the excellent agreement between the simulations and the data obtained at 115 km during areocentric longitude ls 65 allows the extraction of the major contributors to the signature with the eastward propagating diurnal waves of wave numbers one to three being the major players significant contributions are also obtained for eastward propagating semidiurnal waves of wave numbers two three and five and diurnal wave number five a sensitivity study is performed to delineate the effects of the near ir tidal forcing of the upper atmosphere on the wave content at those heights simulations without this forcing yield reduced amplitudes for diurnal eastward propagating waves two and three along with a more latitudinally symmetric response for these two components as well as for diurnal eastward propagating wave number one

density variability at scales typical of gravity waves observed in mars thermosphere by the mgs accelerometer 1 examination of the small scale density perturbations in mars thermosphere inferred from mars global surveyor mgs accelerometer data reveals wave like structures consistent with gravity waves the structures are interpreted to be horizontal with dominant wavelengths of 100 300 km observed along the orbital path density perturbations are significantly stronger in winter versus spring summer suggesting that the zonal mean winds play a major role in filtering these waves there is also evidence of possible modulation by the mean winds due to local time differences no correlation is found with the underlying topography a source region on earth for gravity waves in fact density perturbations in the northern hemisphere are observed to be greater than those in the southern hemisphere which has a higher orographic variance over the martian tropics an observed source region for gravity waves density perturbations are again not elevated leaving questions on how gravity waves observed in the lower atmosphere are related to those observed in the thermosphere

impact of gravity waves on the middle atmosphere of mars a non orographic gravity wave parameterization based on global climate modeling and mcs observations the impact of gravity waves gw on diurnal tides and the global circulation in the middle upper atmosphere of mars is investigated using a general circulation model gcm we have implemented a stochastic parameterization of non orographic gw into the laboratoire de meteorologie dynamique lmd mars gcm lmd mgcm following an innovative approach the source is assumed to be located above typical convective cells urn x wiley jgre media jgre21298 jgre21298 math 0001250 pa and the effect of gw on the circulation and predicted thermal structure above 1 pa urn x wiley jgre media jgre21298 jgre21298 math 000250 km is analyzed we focus on the comparison between model simulations and observations by the mars climate sounder mcs on board mars reconnaissance orbiter during martian year 29 mcs data provide the only systematic measurements of the martian mesosphere up to 80 km to date the primary effect of gw is to damp the thermal tides by reducing the diurnal oscillation of the meridional and zonal winds the gw drag reaches magnitudes of the order of 1 m s sol above 10 urn x wiley jgre media jgre21298 jgre21298 math 0003 pa in the northern hemisphere winter solstice and produces major changes in the zonal wind field from tens to hundreds of m s while the impact on the temperature field is relatively moderate 10 20 k it suggests that gw induced alteration of the meridional flow is the main responsible for the simulated temperature variation the results also show that with the gw scheme included the maximum day night temperature difference due to the diurnal tide is around 10 k and the peak of the tide is shifted toward lower altitudes in better agreement with mcs observations

age and temperature of shock metamorphism of martian meteorite los angeles from u th he thermochronometry mineralogic features attributed to impact induced shock metamorphism are commonly observed in meteorites and terrestrial impact craters partly because the duration of shock metamorphism is very short constraining the timing and temperature of shock events has been problematic we measured u th he ages of single grains of merrillite and chlorapatite from the martian meteorite los angeles la merrillite and chlorapatite ages cluster at 3 28 6 0 15 ma 2s and 2 18 6 0 19 2s ma respectively the mean age of the merrillites which are larger than chlorapatites is indistinguishable from cosmic ray exposure ages 3 1 6 0 2 ma suggesting that impact induced shock metamorphism was coeval with ejection of the la precursor from mars to constrain the initial temperature of shock metamorphism in the la precursor body we modeled diffusive loss of he from merrillite as a function of diffusion domain size la precursor body size and ablation depth from these calculations we suggest that the metamorphic temperature of the shock event was higher than 450 8c these results support the idea that shock pressures of the martian meteorite shergotty were higher than 45 gpa as inferred from the presence of post stishovite sio2 polymorphs single grain u th he dating of phosphates may provide unique constraints on the timing and pressure temperature dynamics of shock metamorphism in a wide variety of extraterrestrial materials

constraining the timing of brittle deformation and faulting in the toki granite central japan abstract constraining of the timing of fault zone formation is of fundamental geotectonic importance to understand structural evolution and brittle fault processes here we present authigenic illite k ar age data from brittle fault zones comprising two gouges within the toki granite central japan the gouge samples were collected at depths of 252 9 and 403 7 m from a shaft at the mizunami underground research laboratory and were separated into five grain size fractions

cenozoic denudation of corsica in response to ligurian and tyrrhenian extension results from apatite fission track thermochronology 1 the island of corsica france occupies a unique position in the western mediterranean since it has recorded both the cenozoic alpine orogenic history of the area as well as subsequent extensional collapse and oceanic basin formation we present 41 new apatite fission track aft ages and 23 measurements of track length distributions from corsica in order to elucidate its cenozoic thermal and morphological evolution aft ages vary from 10 5 0 8 ma to 53 8 4 1 ma and form a clear spatial pattern oldest ages are encountered in the southwest of the island with a broad band of ages between 20 and 30 ma running across the mountainous central area and ages 20 ma confined to the eastern half of the island samples along the western and northwestern coasts record kilometer scale erosional denudation linked to rifting in the ligurian provencal basin whereas samples from close to the extensionally inverted alpine deformation front record a later cooling phase related to tyrrhenian extension the eastward younging pattern of aft ages suggests the migration of a wave of erosional denudation from west to east across the island apparently controlled by the migrating locus of extension our aft data therefore support models of mediterranean extension controlled by slab roll back

inversion of apatite fission track data for thermal history information apatite fission track length distributions and ages provide an integrated record of the low temperature 20 150 c thermal history of the host rock over geologic time scales the information content of these data is quantified by applying a stochastic optimization technique simulated annealing to determine the range of thermal histories compatible with synthetic apatite fission track data given a mathematical description of fission track annealing the goodness of fit between the observed and predicted data parameters and a slowly decreasing control parameter are treated as analogous to the free energy and temperature respectively of a thermodynamic system on this basis a boltzmann type probability distribution is defined and used to accept or reject random thermal history perturbations a priori information used to constrain the model space may include the temperature range in which the solutions are sought present day temperature the complexity of the thermal history and the maximum duration of the data sensitive thermal history this approach allows determination of the range of thermal histories compatible with an observed confined track length distribution and associated fission track age and it provides an estimate of the probability distribution of temperatures at a specific time results for synthetic data sets for diverse model thermal histories suggest that the resolution of thermal history is generally poor parts of the thermal history to which the data are most sensitive can be resolved to no better than about 10 c for ideal data bounds on acceptable time temperature space are sensitive to the assumed complexity of the thermal history but are relatively insensitive to typical uncertainties associated with the data application of this approach to real data is fundamentally limited by the uncertainty associated with extrapolating annealing models to geologic conditions

subsurface temperature distributions in south texas abstract isothermal surfaces and temperature gradients confirm the presence of anomalously high geothermal gradients within south texas we have analyzed 2200 oil and gas well logs and compiled more than 5200 corrected bottom hole temperature measurements the data show that temperature gradients often steepen from around 1 5 f 100 ft to 3 4 f 100 ft 30 c km up to 60 c km near the top of geopressure 0 7 psi ft or 15 8 kpa m from 6 000 to 12 000 ft 1 830 to 3 660 m throughout much of the south texas gulf coast however the highest gradients coincide with the wilcox growth fault zone within the wilcox trend isotherms indicate that the elevated temperatures become more prominent with depth our qualitative analyses indicate that the thermal anomaly is caused by advecting fluids moving upward along and just coastward of the wilcox fault zone in addition preliminary computer modeling indicates that a pulse or pulses of deep upwelling fluids could create the anomalous temperatures petrographic and geochemical data are also consistent with enhanced fluid flux in the zones of elevated temperatures as are the distributions of hydrocarbon and uranium deposits higher temperatures also exist above the top of geopressure along the wilcox trend this suggests that fluids are escaping from the geopressured zone via growth faults and perturbing the temperature field in the overlying meteoric regime although a few areas of the vicksburg frio growth fault zones have elevated temperature gradients below the top of geopressure it is still unknown why such a prominent thermal anomaly occurs along the wilcox trend but not along the vicksburg frio trends

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data