valles marineris dune sediment provenance and pathways abstract although low albedo sand is a prevalent component of the martian surface sources and pathways of the sands are uncertain as one of the principal present day martian sediment sinks the valles marineris vm rift system hosts a diversity of dune field populations associated with a variety of landforms that serve as potential sediment sources including spur and gully walls interior layered deposits ilds and landslides here we test the hypothesis that vm dune fields are largely derived from a variety of local and regional intra rift sediment sources results show several dune fields are superposed on ancient wall massifs and ilds that are topographically isolated from extra rift sand sources spectral analysis of dune sand reveals compositional heterogeneity at the basinal dune field and dune scales arguing for discrete relatively unmixed sediment sources in coprates and melas chasmata mapping is consistent with the principle sand source for dunes being noachian aged upper and lower wall materials composed of primary igneous minerals and glasses some of which show evidence for alteration in contrast dune fields in capri juventae and ganges chasmata show evidence for partial sediment derivation from adjacent early hesperian aged hydrated sulfate bearing ild units this finding indicates that these ilds act as secondary sand sources dunes containing soft secondary minerals e g monohydrated sulfate are unlikely to have been derived from distant sources due to the physical weathering of sand grains during transport isolated extra rift dune fields sand sheets and sand patches are located on the plateaus surrounding vm and the adjoining areas but do not form interconnected networks of sand pathways into the rift if past wind regimes with respect to directionality and seasonality were consistent with more recent regimes inferred from morphological analysis i e dune slip faces wind streaks and were sufficient in strength and duration small dune populations within aurorae chaos and north of eastern vm might have resulted from extended sand pathways into vm however we favor local and regional derivation of dune sand from a variety of intra rift lithologic sources for most cases dune sand sources and the mechanism by which the sand is liberated are discussed in the context of findings described herein but are broadly applicable to analysis of sediment production elsewhere on mars

seasonal activity and morphological changes in martian gullies abstract recent studies of martian dune and non dune gullies have suggested a seasonal control on present day gully activity the timing of current gully activity especially activity involving the formation or modification of channels which commonly have been taken as evidence of fluvial processes has important implications regarding likely gully formation processes and necessary environmental conditions in this study we describe the results of frequent meter scale monitoring of several active gully sites by the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro the aim is to better assess the scope and nature of current morphological changes and to provide improved constraints on timing of gully activity on both dune and non dune slopes our observations indicate that 1 gully formation on mars is ongoing today and 2 the most significant morphological changes are strongly associated with seasonal frost and defrosting activity observed changes include formation of all major components of typical gully landforms although we have not observed alcove formation in coherent bedrock these results reduce the need to invoke recent climate change or present day groundwater seepage to explain the many martian gullies with pristine appearance

higher order eccentricity cycles of the middle and late miocene climatic variations although there is evidence for milankovitch cycles in deep sea sediments from the pleistocene1 4 and upper miocene5 the origin of orbital eccentricity cycles in these records is controversial5 14 recent spectral analyses15 16 of non glacial climatic records of mid cretaceous and early mesozoic exhibit the dominance of 100 and 400 kyr eccentricity cycles and exclude the possibility that the above periodicities originate from the internal variability of ice sheets here i present the walsh spectrum analyses of 10 myr oxygen 18o and carbonate 13c isotope variations spanning the middle and late miocene which reveal statistically significant periodicities of approximately 2 0 and 1 25 myr 800 400 115 and 93 kyr and harmonics of the higher order terms with remarkable resolution higher order periodicities hitherto unexplained in the spectrum of deep sea records match quite well with predicted large eccentricity cycles in the earth s orbital variations17 indicating that eccentricity forcing induced by orbital variations exerts a major influence on the earth s climate

event stratigraphy and paleoceanography in the fortuna basin southeast spain a scenario for the messinian salinity crisis the timing and duration of evaporitic deposition during the messinian in the mediterranean is poorly known to assist with this problem we have correlated sedimentological events at widely separated locations in the mediterranean and dated paleoceanographic events in the world ocean event stratigraphy our working hypothesis is as follows the messinian salinity crisis caused the formation of evaporites in a deep desiccated basin which implies that 1 the evaporites were deposited during a steady marine influx 2 multiple intervals of isolation led to drastic changes in the sediments and in the fauna of the mediterranean 3 the sea level of the mediterranean sea was mostly several hundreds of meters below that of the atlantic ocean and 4 the seaways betic and rif strait connecting the mediterranean with the atlantic during the late miocene were affected by eustatic sea level changes caused by antarctic glaciation we found supporting evidence in the sedimentological and paleoceanographic records in the betic strait fortuna and sorbas basins which was one of the sites of major inflow into the late miocene mediterranean sea drastic sea level changes and fluctuations during the late tortonian and messinian caused chronologically 1 the deposition of brackish sediments overlying marine deposits 2 the progradation of deltas 3 reef growth at lower levels and their destruction by erosion and coverage by conglomerates 4 evaporite deposition alternating with marine marls containing atlantic diatom assemblages and 5 five marine terrestrial cycles associated with coral reefs based on event stratigraphy the following scenario for the messinian salinity crisis is proposed the tripoli formation chron 6r1 5n2 5 93 5 7 ma the lower evaporites chron 5n2 5r 5 7 5 5 ma and the upper evaporites lowermost gilbert c 5 25 5 15 ma were deposited during influx of atlantic water into the mediterranean during this time a unidirectional circulation dominated from the atlantic through the betic strait only during the intra messinian inundation chron 5n1 into lowermost gilbert c 5 4 5 25 ma that occurred after a short intra messinian erosional event chron 5n1 5 5 5 4 ma was a normal bidirectional circulation pattern established this is reflected in the diatomites of the chicamo formation and the mediterranean site 124 as well as most likely in a reef on cyprus the marine record of the pliocene filling of the mediterranean is missing in these basins overall marine water inflow into the mediterranean through the betic strait dominated during the messinian the threefold marine terrestrial cyclicity with severe paleoceanographic changes in the fortuna and sorbas basins favor the deep desiccated basin model

evaporitic mixed water dolomitization on st croix u s v i abstract dolomite exists in only a small area of pliocene carbonates on st croix this area consists of reef lagoonal and platform facies that underlie and rim the shoreline of krause lagoon an embayment that existed on the southern coastline of st croix prior to industrial development in the 1960s since dolomite is not found in similar facies elsewhere on st croix this geographic distribution suggests that the formation of the dolomite was related to hydrologic conditions in krause lagoon the dolomite is calcium rich 57 60 mol ca and exists both as euhedral rhombs 2 75 m in diameter and as a replacement mineral in dolomitized bioclasts bioclasts in the dolomitic strata often show good preservation of microstructure particularly in large benthic forams and coralline algae the mean 87sr 86sr isotopic composition of the dolomite is 0 70887 0 00002 2s n 3 which corresponds to the 87sr 86sr ratio of late miocene seawater however because the dolomite resides in pliocene strata it is difficult to invoke unmodified seawater as an agent of dolomitization dolomitization therefore requires a source of nonradiogenic strontium modern st croix groundwater has 87sr 86sr compositions between 0 7076 and 0 7085 n 4 well below the ratio of both modern seawater and the dolomites mixing calculations show that modern st croix groundwater could be a significant source of nonradiogenic strontium in a dolomite formed f om a two component groundwater seawater mix on the basis of strontium concentration modeling the groundwater component responsible for the st croix dolomites may have ranged from 40 to 80 of the dolomitizing fluids stable isotopic values for the dolomite range from d18o of 0 7 to 3 8 and d13c of 0 6 to 2 4 pdb with increasing d18o and d13c values from the margins to the center of the lagoon the maximum d18o values in these dolomites are too high to have formed fro unaltered groundwater or seawater even accounting for ice volume effects therefore the isotopically heaviest dolomite must have precipitated from fluids enriched in 18o probably as a result of evaporation dolomitization from fluids produced from a mixture of evaporated seawater and st croix groundwater are consistent with the geochemistry and geologic distribution of the dolomite calculations show that such a scenario is possible and may be fairly common despite the relative complexity of the model documented block faulting of the krause lagoon area may have provided a stable hydrologic regime for a long enough time for dolomite to form despite island uplift during the late tertiary other models of dolomitization can be shown to be less likely or untenable on the basis of chemical lithologic or hydrologic criteria

revised age estimates of brunhes palaeomagnetic events support for a link between geomagnetism and eccentricity revisions in the dates of reported geomagnetic excursions during the brunhes epoch are proposed in light of possible correlations between a section at gioia tauro italy deep sea cores a core from lake biwa japan and some lava flows the anomalously long double blake event reported at gioia tauro is here correlated with the blake event 110 kyr and the biwa 1 event 180 5 kyr an hiatus may be present in the section between these two events the event at gioia tauro is correlated with the biwa 2 event at about 295 kyr the event with the biwa 3 event at about 400 kyr the event with the snake river event at 480 50 and the event not recorded elsewhere is estimated to have occurred at 620 kyr these proposed refinements in the age estimates of the excursions suggest an approximately 100 kyr cyclicity if the events are real and the revised dating is correct the timing of the geomagnetic events seems to coincide with times of peak eccentricity of the earth s orbit suggesting a causal connection

a boundary layer model for mars comparison with viking lander and entry data abstract a one dimensional boundary layer model for mars is described and its results are compared with viking data the model equations are similar to earth boundary layer models in that they include contributions from coriolis pressure gradient and frictional forces for momentum and radiation sensible heat flux convergence and advection for heat turbulent fluxes are computed from the level 2 second order closure theory of mellor and yamada with similarity relations employed for boundary conditions the pressure gradient force can be specified or computed from a simple slope model radiative heating is due to the absorption of solar and infrared radiation by co2 gas and suspended dust particles ground temperatures are computed by solving a surface heat budget using an accurate treatment of conduction into the martian soil the data used for comparison were obtained by the viking 1 and 2 landers for early northern summer at each site these data include a single profile of wind and temperature be

western boundary currents in the atmosphere of mars western boundary currents wbcs are an intensification of north south flow adjacent to an eastward facing meridional boundary although most familiar in the oceans where the gulf stream is the best known example wbcs also occur in the earth s troposphere the main example being the east african jet1 which is thought to play an important role in the asiatic monsoon here we identify boundary currents in a different geophysical context a numerical simulation of the atmosphere of mars in our simulation wbcs exist in association with significant cross equatorial flow and the presence of equatorial martian topography which has vertical scale far exceeding terrestrial relief2 the intensity and width of these currents depend on model parameters notably the surface drag from a comparison of our results with other martian models we suggest that wbcs have already been simulated although they were not previously identified as such3 the available observational evidence appears to be consistent with the presence of martian wbcs which may be important in the generation of global and great dust storms

sr s and oso4 isotopes and the depositional environments of the upper miocene evaporites spain abstract upper miocene evaporites in the nijar basin southeastern spain contain thick massive and coarse crystalline selenites of the middle messinian yesares formation on the basis of their sedimentary fabrics and structures such as euhedral terminations of crystals well preserved algal filament inclusions and standing growth orientations these selenites are interpreted to be primary bottom growth deposits most of these selenites have sr concentrations of about 1000 ppm range from 700 to 1800 ppm 87sr 86sr values of yesares selenites vary between 0 70890 and 0 70896 n 18 which are all within the known range of messinian seawater suggesting a marine origin however quantitative modeling of 87sr 86sr vs sr ca of fluids demonstrates that a minor amount of admixed nonmarine fluid e g 20 might have contributed to the yesares marine brines 34s and 18oso4 values of yesares selenites range from 21 to 24 cdt and from 10 to 16 smow respectively these ranges are more variable and most values are heavier than those expected for normal miocene marine gypsum on the basis of quantitative modeling these heavy 34s and 18oso4 values have most likely resulted from reduction and oxidation reactions of sulfur species that occurred in brines rather than from contributions of nonmarine water or from reservoir crystallization effects the use of sr s and o isotopes provides a possible means of distinguishing whether an ancient evaporite was deposited by marine nonmarine or hybrid brines sr isotopes however are insensitive to minor nonmarine contributions on the basis of quantitative modeling and consequently marine sr isotopes for evaporites e g gypsum do not necessarily indicate pure marine depositional environments compared to sr isotopes 34s and 18oso4 of marine gypsum are even more insensitive to minor nonmarine contributions because of much higher so4 concentrations in seawater and seawater evaporated brines than in most freshwaters therefore sr o and s isotopes should be used with caution to interpret depositional environments and to determine parent fluids of ancient evaporites

apparent correlation of palaeomagnetic intensity and climatic records in deep sea sediments most reports of a correlation between pleistocene climate and geomagnetic field intensity rely strongly on the assumption that sediment natural remanent magnetic nrm intensity provides a record of geomagnetic field strength and is not sensitive to local changes in properties of the sediment critical assessment of relevant data presented here and elsewhere1 2 from deep sea sediment cores shows that a pronounced dependence of nrm intensity on sediment composition can occur which implies that this assumption is unlikely to be generally valid as sediment composition often reflects varying depositional conditions induced by climatic change the significance of correlations proposed between pleistocene palaeomagnetism and climatic indicators in deep sea sediments may be less dramatic than sometimes supposed

structure and dynamics of the convective boundary layer on mars as inferred from large eddy simulations and remote sensing measurements the structure of the martian convective boundary layer bl is decribed by means of a novel approach involving both modelling and data analysis mars express radio occultation ro temperature profiles are compared to large eddy simulations less performed with the martian mesoscale model the model combines the martian radiative transfer soil and surface layer schemes designed at laboratoire de meteorologie dynamique lmd with the most recent version of the weather research and forecast wrf fully compressible non hydrostatic dynamical core the key roles of the vertical resolution and to lesser extent of the domain horizontal extent have been investigated to ensure the robustness of the les results the dramatic regional variations of the bl depth are quantitatively reproduced by the martian les intense bl dynamics are found to underlie the measured depths up to 9 km vertical speed up to 20 m s 1 heat flux up to 2 7 k m s 1 and turbulent kinetic energy up to 26 m2 s 2 under specific conditions both the model and the measurements show a distinctive positive correlation between surface topography and bl depth our interpretation is that in the tenuous co2 martian near surface environment the daytime bl is to first order controlled by the infrared radiative heating fairly independent of elevation which implies a simple correlation between the bl potential temperature and the inverse pressure pressure effect no prominent pressure effect is in action on earth where sensible heat flux dominates the bl energy budget both ro observations and numerical simulations confirm the terrain following behaviour of near surface temperature on mars induced by the dominant radiative influence the contribution of the martian sensible heat flux is not negligible and results in a given isotherm in the bl being comparatively closer to the ground at higher surface elevation the strong radiative control of the martian convective bl implies a generalised formulation for the bl dimensionless quantities based on this formulation and the variety of simulated bl depths by the les new similarity relationships for the martian convective bl in quasi steady midday conditions are derived rigorous comparisons between the martian and terrestrial bl and fast computations of the mean martian bl turbulent statistics are now made possible by such similarity laws copyright 2010 royal meteorological society

martian surface winds insensitivity to orbital changes and implications for aeolian processes aeolian features observed on the surface of mars provide insight into current and potentially past surface wind systems in some cases the features are clearly transient and related to the lifting and settling of atmospheric dust other features like dunefields yardangs and ventifacts are more persistent and likely require significant time to form in this study we analyze the observed directions of selected aeolian features with the aid of the geophysical fluid dynamics laboratory mars general circulation model gcm initially we examine bright and dark streaks which have been observed to form in association with global dust storms the ability to match these features with mars gcm wind directions provides an important validation of the model more important we are able to define best fit seasons and local times for both types of features which provide the basis for extension and modification of the veverka et al 1981 model of bright and dark dust streak formation in addition these best fit times correspond well with the dark streak wind storm model of magalhaes and young 1995 the primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long term wind indicators for example the misalignment of rock tail and ventifact orientations at the mars pathfinder landing site specifically we assess whether changes in planetary obliquity precession or global dust opacity could significantly alter patterns of surface wind directions in all cases we find the seasonal and annual average wind direction patterns to be highly invariable while changes in the dust loading hence the partitioning of solar absorption between the surface and atmosphere and in the surface latitude of maximum solstitial insolation cause the vigor of the large scale circulation to increase especially the hadley cell the spatial patterns of the surface wind orientations remain essentially unchanged in the case of perihelion during northern summer opposite of the current perihelion position the northern summer hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere taken together these results cast significant doubt on orbital explanations for surface wind changes it is thus suggested that significant changes in topography e g tharsis uplift true polar wander or climate e g the existence of a significantly thicker atmosphere or an ocean at some point in the past are more likely explanations for long term wind indicators such as the ventifact orientations at the mars pathfinder landing site

extracting mg isotope signatures of ancient seawater from marine halite a reconnaissance abstract the mg ca ratio of seawater fluctuated remarkably over the phanerozoic the processes that controlled the temporal variation in seawater mg ca ratio may also have caused the secular changes in mg isotope ratios of seawater therefore the mg isotope composition of seawater may be useful to understand the long term variation in seawater chemistry different sedimentary carbonates have been proposed as archives of ancient seawater mg isotope signatures but each type of carbonate has its limitations halite is a common mineral in evaporite deposits and their fluid inclusions may be used to infer the mg isotope composition of contemporary seawater in this study we developed a method to measure the isotope composition of mg in halite with an accuracy of better than 0 1 in 26mg the accuracy of the method was verified systematically using synthetic nacl solutions as well as holocene lacustrine halite samples from the dead sea the 26mg values of marine halite samples show a large variation ranging from 0 1 to 1 6 relative to the dsm3 international mg isotope standard the 26mg values of some ancient salt samples are lower than a published model curve for 26mg of seawater and such inconsistency could be explained by 1 isotopic evolution of brines due to mineral precipitation 2 entrapment of evaporite minerals into halite during halite precipitation or post depositional deformation 3 recrystallization and dissolution of pre existing mg minerals and 4 limitations of the model curve of seawater 26mg values collectively we suggest that mg isotopes in halite are a new geochemical proxy to study the secular variations in seawater chemistry syndepositional and post depositional processes of evaporite deposits our data highlight the importance of understanding the sedimentary background and textural details of evaporites for appropriate interpretations of mg isotope data from halite

meteorology of proposed mars exploration rover landing sites 1 a descriptive study of the near surface meteorology at three of the potential mars exploration rover mer landing sites terra meridiani gusev crater and melas chasma is presented using global and mesoscale models the mesoscale model provides a detailed picture of meteorology on scales down to a few kilometers but is not well constrained by observations away from the viking and pathfinder landing sites as such care must be taken in the interpretation of the results with there being high confidence that the types of circulations predicted will indeed occur and somewhat less in the quantitative precision of the predictions and the local time phasing of predicted circulations all three landing sites are in the tropics and are affected by hadley circulation by diurnal variations due to the global thermal tide and by planetary scale topography in these particular cases from tharsis elysium and the global topographic dichotomy boundary terra meridiani is least affected by large variations in local topography mean winds at terra meridiani during mer landing would be less than 10 m s with little vertical shear however these low wind speeds result from strong mixing in the early afternoon convective boundary layer which creates its own hazard in the horizontal variation of vertical winds of up to 8 m s both upward and downward in gusev crater the topography of ma adim vallis and the crater rim generates strong diurnally reversing channeling of wind in ma adim vallis and diurnally reversing radial flow in the crater associated with thermal slope winds on the crater rim the overturning circulation in gusev crater slightly suppresses the daytime convective boundary layer melas chasma in valles marineris provides an example of strong topographic forcing of near surface circulation of particular interest is the channeling of regional scale wind toward the center of the tharsis plateau during the evening this results in a surface level jet along the canyon of over 25 m s drainage of air from the plateau and into the canyon produces vertical winds down the canyon walls in the evening of over 5 m s in contrast during the early afternoon mer landing time horizontal winds at the proposed mer landing site are relatively calm with little mean shear with height this results from the proposed site being in a region of local divergence and the action of daytime convection the nature of flow in melas chasma results in an interesting dual maximum in boundary convection and depth with the usual daytime afternoon free convective maximum being joined by a mechanically forced nighttime boundary layer of almost 2 km depth

convergent crater circulations on mars influence on the surface pressure cycle and the depth of the convective boundary layer modeling of slope flow circulations in idealized axisymmetric craters is used to understand 1 the large surface pressure amplitude observed in gale crater by the rover environmental monitoring station and 2 the shallow convective boundary layer cbl suggested by curiosity imagery air temperatures vary within craters with greater amplitudes than outside them becoming warmer colder during day night this crater circulation effect is most significant over the depth of the crater key parameter within the idealized craters a surface pressure cycle develops in the real atmosphere it is enhanced partially caused by thermal expansion a surge of mass away from the craters develops during daytime over crater floors the cbl depth is inhibited by a capping inversion from the adiabatic warming of widespread daytime subsidence for a variety of craters radius depth and with or without a central mound the results are very similar in real atmosphere simulations over canyons or large basins similar circulations are seen

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

pinning points a method providing quantitative constraints on relative sea level history abstract quantitative constraints on the history of relative sea level allow for a better understanding of the controls on depositional sequence development the constraints are provided by pinning point curves plots of ancient relative sea level elevations pinning points versus time constructing a pinning point curve requires identification of ancient stratigraphic positions of sea level through interpretation of facies and surfaces formed at sea level then their ancient relative elevations are determined through reconstructing aspects of ancient paleotopography upper miocene strata from las negras southeastern spain preserve paleotopography contain ancient surfaces of subaerial exposure and contain facies deposited near sea level the pinning point curve illustrates a complex relative sea level history with large and small scale relative sea level fluctuations defined by 31 pinning points

growth demise and dolomitization of miocene carbonate platforms on the marion plateau offshore ne australia abstract strontium isotope stratigraphy has been used to examine the timing of depositional events and dolomitization in two miocene carbonate platforms cored by ocean drilling program odp leg 194 just seaward of the great barrier reef the results provide firm constraints for correlating surfaces and depositional stages between the two platforms and thereby relating seismic sequences previously defined in the off platform sediments to the lithostratigraphic units described from cores in the seismically transparent platform top sites oyster bearing beds at the base of both platform successions yield early oligocene ages 29 31 ma thus dating initial transgression of the marion plateau s volcanic basement there followed a period of slow accumulation of shallow water grainstones rich in quartz and phosphate grains in late oligocene time 29 23 ma seismic megasequence a the main growth of the carbonate platforms took place in early to late miocene time 23 7 ma comprising five depositional sequences the first four of these seismic megasequence b are common to both platforms and terminated with a possible karst surface at 10 7 ma different sedimentologic expression of this megasequence in the two platforms reflects contrasting progradational versus aggradational geometries in the locations studied the final growth stage seismic megasequence c occurred only in the southern platform and terminated at 6 9 ma both platform demise events 10 7 and 6 9 ma approximately coincide with falls in global sea level combined with longer term trends of decreasing water temperature sr isotope ages of dolostones increase with depositional age and older dolostones in the southern platform have more coarsely crystalline and fabric destructive textures than overlying younger dolostones these relationships are consistent with dolomitization by normal seawater shortly after deposition and overprinting of multiple times of dolomite recrystallization and cementation in the deeper strata

numerical models of fluid flow in carbonate platforms implications for dolomitization abstract the role of fluid flow in dolomitization is evaluated through hydrologic simulations designed to capture and test numerically the essential elements of some common dolomitization models a two dimensional finite difference code bethke 1985 was used to simulate single phase flow of variable salinity fluids driven by compaction convection and topography in carbonate platforms and adjacent basinal sediments a simple hydrostratigraphic model consisting of a platform reef complex surrounded by basin filling shale was constructed to examine the magnitude and direction of compaction flow during the initial phase of subsidence most pore fluids in the shale migrate to the surface at velocities less than 0 1 mm yr and basin derived fluids are focused into the reef from only a limited distance of 10 km relatively porous and permeable basinal limestones and sandstones may act as conduits for updip fluid flow into the platform reef complex magnesium mass balance constraints coupled with hydrologic simulations suggest that burial compaction is not an efficient mechanism for regional dolomitization two layer hydrostratigraphic models involving variable salinity fluids show that evaporation of seawater results in downward and seaward fluid migration the magnitude of flow is a function of fluid density even fluids at salinities marginally elevated above normal seawater values are capable of penetration several hundreds of meters into the underlying sediments albeit at rates of less than 1 cm yr paleohydrologic simulations coupled with thermodynamic arguments support that reflux of surface derived waters evaporated past gypsum saturation is a viable dolomitization mechanism calculations utilizing rates of mg mass flux show that dolomitization of large carbonate platforms 10 km3 by fluids below halite saturation requires millions of years of reflux driven flow p thermal convection of seawater through carbonate platforms has been simulated by varying the basal heat flow the thermal pump produces a convection cell in which lateral and vertical flow achieve rates of 75 0 and 13 0 mm yr respectively the potential for dolomitization is high because a large reservoir of mg seawater is tapped elevated temperatures drive fluids further into the stability field for dolomite and kinetic inhibition of dolomite nucleation and growth is decreased simulations of high frequency glacio eustatic sea level oscillations suggest that a dynamic hydrologic regime may be established a sea level fall of 2 m lasting for 10 000 yr can drive lateral flow at rates up to 0 15 m yr dolomitization is possible because marine waters migrate through the carbonate platform in response to gradients of hydraulic head created by eustatic sea level fluctuations

early dolomitization and recrystallization of the lower middle ordovician carbonates in western tarim basin nw china abstract the lower middle ordovician shallow marine carbonates in western tarim basin were dolomitized to different degrees the resultant dolomites are mainly concentrated in the successions of platform interior to shallow subtidal shoal and display an upward decrease in abundance based on petrographic textures three types of matrix dolomites were identified 1 very finely to finely crystalline nonplanar a to planar s dolomite md1 2 finely to medium crystalline planar e s dolomite md2 and 3 finely to coarsely crystalline nonplanar a dolomite md3 origins of matrix dolomites are interpreted on the basis of field investigation petrography and isotopic o c and sr geochemistry md1 dolomite was formed from slightly evaporated i e mesosaline to penesaline seawater in near surface to very shallow burial settings possibly facilitated by microbial mediation i e bacterial sulphate reduction bsr md2 dolomite was precipitated from connate seawater stored in coeval limestone in shallow burial realms in contrast md3 dolomite was likely formed as a consequence of intense recrystallization of early formed dolomites e g md1 at depths the formation of early matrix dolomites i e md1 was likely determined by depositional facies and sea level variations of variable orders this study provides a useful analogue to understand the dolomitization processes related to depositional facies and variable order sea level fluctuations in the tarim basin and elsewhere

mars atmospheric winds indicated by motion of the viking landers during parachute descent winds in the martian atmosphere at altitudes from 1 5 to 3 5 km have been determined from parachute descent trajectories of the two viking landers viking 2 reached equilibrium with nearly steady winds of 8 m s to the southeast below 3 3 km at 1000 lt viking 1 winds at 1615 lt rotated clockwise with decreasing altitude but were generally to the northwest at 20 m s at 1 5 km the viking 1 wind direction was close to that measured by the landed anemometer at the same local time while at the viking 2 site wind direction at 1 5 km was nearly opposite that near the surface this is consistent with the fact that viking 1 descended within a vigorously convective boundary layer while viking 2 at 1 5 km was above the boundary layer turbulent velocities in the viking 1 boundary layer were 3 m s mean upflow velocity was 1 m s the viking 2 atmosphere was relatively quiescent with orderly wind directional variation possibly suggesting the presence of waves comparison of the measured winds with a recent global circulation model showed little or no correspondence probably an indication that the winds were locally controlled the boundary layer slope wind model of haberle et al 1993 with ground slope adjusted to give best fit to these and landed meteorology data gave roughly the wind direction and the observed magnitude within a factor of 2 but with opposite rotation of the wind vector with altitude the ground slopes deduced are consistent with terrain observed in approach to the viking 1 landing and do not conflict with the less definitive terrain data at the viking 2 site the high sensitivity of winds at altitudes up to several kilometers to terrain slopes as small as a few meters per kilometer would suggest that slope winds may be widely found in the lowest few kilometers of mars atmosphere

ascending freshwater mesohaline mixing a new scenario for dolomitization abstract the process of mixing zone dolomitization has received enough criticism in recent years to suggest that it no longer be considered viable for making large amounts of dolomite this study proposes an alternative model that still requires fluid mixing in this model ascending flow of freshwater mixes with evaporated seawater leading to extensive dolomitization the new model is constrained by data from upper miocene strata of southeast spain where dolomite yields fluid inclusion tm ice data that range from 0 2 to 2 3 c indicating precipitation from fluids of 4 to 43 ppt seawater salt equivalent thus confirming fluid mixing the 13c and 18o of the dolomite ranges from 4 5 to 3 0 vpdb and 0 9 to 6 0 vpdb respectively and displays positive covariance although such positive covariation may represent fluid mixing the mixing of two dolomites during sampling or an originally homogeneous dolomite that has been partially altered recrystallized fluid inclusion data and cathodoluminescence petrography disprove the mixture during sampling and partial alteration hypotheses modeling of the most positive dolomite 18o values indicates an evaporated seawater endmember of 43 ppt salinity identical to that of the most saline fluid inclusions because paleotopography is preserved in the study area the spatial variation in dolomite geochemistry can be mapped to evaluate if it is consistent with the hydrogeology of a typical mixing zone model or an alternative the data reveal that both downdip and updip areas were influenced by high salinity and low salinity fluid endmembers and that stratigraphically lower units have more depleted 13c and 18o than upper units these results are consistent with a model of upward flow of freshwater that provides the mechanism of mixing of freshwater and evaporated seawater upward flow and degassing of co2 from loss of pressure contributed to nearly platform wide dolomitization in this succession and may have analogs in other ancient successions

the martian daytime convective boundary layer results from radio occultation measurements and a mesoscale model abstract we investigate the behavior of the martian daytime convective boundary layer cbl through a combination of data analysis and modeling this study relies on two subsets of mars express radio occultation ro measurements that sounded the atmosphere in northern spring of successive mars years only the first year of observations has been examined previously hinson et al 2008 the second year provides complementary spatial coverage and greatly increases the total number of observations analysis of the ro profiles yields basic characteristics of the cbl such as its depth d and the average potential temperature of the mixed layer m we also combine ro retrievals of surface pressure with surface temperatures from infrared sounding to characterize the surface forcing expressing the result as a potential temperature s these observations are at local times in early afternoon for s and late afternoon for m and d when each parameter is near its diurnal maximum we use measurements at mid to low latitudes which sample a wide range of s 227 294 k to determine the response of the lower atmosphere to spatial variations in surface forcing the depth of the cbl ranges from less than 3 km in the midlatitude topographic basins to more than 9 km above elevated terrain in the tropics the dependence of m on s is linear with a characteristic slope of about 0 7 in both years we gain further insight by performing a simulation with the oregon state university mars mesoscale model in a region centered on isidis planitia which includes two potential landing sites for the mars 2020 rover as expected from previous modeling of much smaller craters the arc of steep topography along the western and southern margins of isidis produces a distinctive diurnally varying mesoscale circulation the simulation captures key features of the observations such as the wide variations in m and d by 34 k and 9 km respectively that occur within this region the model also accounts for peculiar features of ro profiles on the rim of isidis where the wind field strongly influences the depth and diurnal evolution of the cbl detailed comparisons with the observations validate the general performance of the model and confirm several aspects of the simulated wind field

dolomitization of the middle devonian winnipegosis carbonates in south central saskatchewan canada the middle devonian winnipegosis carbonate unit in south central saskatchewan is partially to completely dolomitized two major types of replacive dolomite are distinguished microcrystalline to finely crystalline dolomite type 1 displays nonplanar a to planar s textures mimetically replaces the precursor limestone accounts for about four fifths of dolomite phases volumetrically and mainly occurs in the winnipegosis mounds and the lower winnipegosis member directly underlying the mounds medium crystalline dolomite type 2 shows planar s to planar e textures commonly occurs in the lower winnipegosis and brightholme members and decreases upward in abundance the 87 sr 86 sr ratios of type 1 dolomite 0ae70795 to 0ae70807 fall within the estimated sr isotopic range for middle devonian marine carbonates stratigraphic petrographic and geochemical data constrain the formation of type 1 dolomite to hypersaline sea water in a near surface environment after marine cementation and sub aerial diagenesis and prior to precipitation of the middle devonian leofnard salts movement of dolomitizing fluids could be driven by density differences and elevation head the shift to lower d 18 o values of type 1 dolomite 7ae 4t o 5ae1 vienna pee dee belemnite vpdb is interpreted as the result of recrystallization at elevated temperatures during burial type 2 dolomite has higher 87 sr 86 sr ratios 0ae70809 0ae70928 suggesting that the dolomite probably formed from basinal fluids with an increased richness in the radiogenic sr isotope in type 2 dolomite sr 2 concentrations are lower and fe 2 and mn 2 concentrations are higher compared with the associated limestone and type 1 dolomite type 2 dolomite is interpreted as having been formed from upward migrating basinal fluids during latest devonian and carboniferous period

the spatial and seasonal distribution of martian clouds and some meteorological implications the spatial and seasonal distributions of martian atmospheric clouds organized according to simple morphologic criteria exhibit distinct patterns when interpreted self consistently using analogies to terrestrial cloud forms and martian temperature wind direction and water vapor measurements patterns of cloud occurrence provide some loose constraints on global scale near surface wind speed static stability and humidity we have examined all mariner 9 and viking orbiter images for this study we concentrate primarily on the larger viking data set whenever observations are possible relatively high near surface winds appear to follow the seasonal cap edges during early fall late winter and spring moderate to high winds are also inferred in mid latitudes for mid southern winter and in low latitudes mainly in the steeply sloping areas of tharsis near the solstices at other times lower winds are suspected hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule cloud occurrence data suggest that the near surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring relatively high static stability is deduced near the winter poles and globally during the dust storm season in spite of low atmospheric temperatures the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid latitudes during early winter during northern spring and summer saturation conditions seem to be easily achieved at mid latitudes and condensate clouds are abundant the situation is complicated by atmospheric dust in southern spring and summer low latitudes generally appear to be farther from saturation than mid latitudes and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons

the role and impact of freshwater seawater mixing zones in the maturation of regional dolomite bodies within the proto floridan aquifer usa palaeogene dolostones from the sub surface of florida are ideal for the study of dolomite maturation because they record the early stages of a secondary dolomite overprint without destruction by later diagenetic overprints two distinct dolomite textures occur in the dolostones of the upper eocene ocala and lower oligocene suwannee limestones in west central florida a porous and permeable sucrosic dolomite and a less porous and relatively impermeable indurated non sucrosic dolomite in both textures the initial matrix dolomite is dully luminescent whereas the secondary overprint is dominantly luminescent cement in the suwannee and only neomorphic luminescent dolomite in the ocala the abundance of luminescent dolomite ranges from 2 to 38 which translates to 1 6 km3 of material in the suwannee and 13 5 km3 in the ocala extrapolated trace element contents sr and na and 18o values for the matrix and luminescent end members indicate a marine origin for the matrix dolomite in both units and a freshwater seawater mixing zone origin for the secondary luminescent dolomites the 18o values indicate that a saline middle mixing zone environment overprinted the suwannee but a more dilute mixing zone affected the ocala fluid fluid mixing models constrained by modern floridan aquifer hydrochemistry and extrapolated 87sr 86sr values of the luminescent phases indicate that the mixing zones operated during the late miocene to pliocene in the ocala and affected the suwannee in the pliocene the luminescent suwannee mixing zone cement reduced porosity up to threefold and permeability up to 100 fold which converted many sucrosic dolomites to indurated dolomites by contrast the neomorphic luminescent ocala dolomite did not have an appreciable impact on the maturations although freshwater seawater mixing zones were not the sites of the initial dolomitization the mixing zone environment did dramatically overprint and mature the regionally widespread dolomites of the ocala and suwannee limestones this maturation occurred shortly after formation of the proto floridan aquifer the timing suggests the matrix dolomites were ripe for alteration and that the only prerequisite for mixing zone dolomite is pre existing dolomite substrates to reduce kinetic barriers in contrast to recent claims the results of this study demonstrate that mixing zones can be effective in forming regionally significant amounts of secondary dolomite and influencing the petrophysical maturation of dolomite bodies

the paleoenvironmental evolution of the cambrian longwangmiao formation stage 4 toyonian on the yangtze platform south china petrographic and geochemical constrains abstract during the cambrian period stage 4 biodiversity and biomass declined rapidly and globally in an event known as the botomian toyonian crisis to gain a better understanding of the paleoenvironment in south china during this stage we present and interpret complex multi parameter carbonate analyses petrography carbon and oxygen isotopic composition and major trace and rare earth elements from the toyonian longwangmiao formation in the bandenggou section the longwangmiao formation comprises primarily carbonate deposits with massive detrital mineral occurrences in its lower middle sequence principal component analysis of the minerals and oxides leads to the definition of two intervals i and ii interval i is composed mainly of dolostones interbedded with sandstones and contains exceedingly high amounts of terrestrial original minerals and oxides as well as high ree y th and sc concentrations interval ii which is composed primarily of limestones has trace amounts of terrestrial original minerals and oxides and low ree y th and sc concentrations the 13c and 18o values show a significant positive shift from interval i to interval ii after eliminating the effects of diagenesis contributions through the analyses of diagenesis sensitive indexes 18o values mgo cao mn sr and fe sr ratios and the correlations of 13c 18o 18o eu eu eu eu ce ce and eu eu feo the sr and na concentrations of calcites in interval i are extremely high exceeding even the corresponding ranges of marine aragonites while calcites from interval ii have low sr and na concentrations that are within the range of marine low mg calcite however both show strong positive correlations between ca sr ca na and sr na the different calcite elemental behaviors in intervals i and ii suggest different carbonate precursors associated with seawater temperature and climate furthermore the sr ca ratios are negatively correlated with 13c and 18o values and the 13c values also negatively correlated with sio2 content these features indicate a significant change in the depositional environment during the cambrian toyonian stage from an early restricted marine environment under a warm and arid climate with massive terrestrial influxes to a later relatively open marine environment under a cool and humid climate with negligible terrestrial influxes this shift likely resulted in the observed changes in biomass and biodiversity

petrologic and geochemical constraints on the origin of subsurface dolomite enewetak atoll an example of dolomitization by normal seawater dolomite is present 1 250 1 400 m below sea level in eocene strata of enewetak atoll petrographically the deep enewetak dolomite postdates brittle compaction of rigid grains in the host eocene strata the 87 sr 86 sr ratio of these dolomites 0 70865 0 70901 indicates that they formed at one or more times between the middle miocene and the present since the top of the lower miocene is more than 900 m above the deep dolomitic interval the dolomite must have formed at a minimum burial depth of 900 m stable oxygen isotope determinations suggest dolomite precipitation from cold marine water lower miocene and eocene carbonate strata on the atoll are apparently in open communication with cold modern ocean water suggesting that those same strata were in open communication with ocean water during dolomitization at a depth of about 1 000 m modern pacific ocean water becomes undersaturated with respect to calcite but is still supersaturated with respect to dolomite therefore it is proposed that the deep enewetak dolomite precipitated from cold deep ocean water undersaturated with respect to calcite at a burial depth of more than 900 m

origin of lower ordovician dolomites in eastern laurentia controls on porosity and implications from geochemistry the catoche formation of the st george group in eastern laurentia western newfoundland consists of early ordovician arenigian shallow marine platform carbonates 160 m thick which were extensively dolomitized during the course of their diagenetic history the dolomites occur as both replacement and pore filling cements and are a major control on porosity distribution in the formation the origin and diagenetic history of the catoche dolomites at daniel s harbour western newfoundland were analysed in comparison to equivalent successions at port au choix pac and port au port peninsula pap to assay the reservoir potential of these dolomites in eastern laurentia petrographic examination identified at least three generations of dolomites in the catoche formation which are 1 an early replacement sub to eu hedral micritic dolomite 4 m 30 m d1 2 eu to sub hedral dolomite 70 m 1 mm often with cloudy cores and clear rims d2 and 3 subhedral to anhedral saddle dolomite cement 200 m 3 mm d3 the micritic dolomite d1 exhibits a dull cathodoluminescence cl under cathodoluminoscope whereas dolomite d2 exhibits consistent concentric cl zonation some subhedral crystals of d3 appear zoned both in plane polarized light and cathodoluminoscope otherwise d3 exhibits a dull cl stoichiometric dolomite occurs in all three generations with d2 as the dominant dolomite by abundance the low strontium 47 25 ppm content coupled with depleted 18o value of dolomitizing fluids 10 to 11 2 vsmow and near micritic grain size suggests an early precipitation of dolomite d1 at low temperatures of near surface conditions from solutions likely formed by mixing of early ordovician sea and meteoric waters in contrast microthermometric measurements of primary two phase fluid inclusions in dolomite d2 homogenization temperatures of 102 168 c with a salinity range of 19 8 25 eq wt nacl and dolomite d3 homogenization temperatures of 158 190 c with a salinity range of 20 2 22 2 eq wt nacl suggest that both dolomite generations were generated in mid to deep burial settings from high salinity low temperature 200 c hydrothermal fluids likely under suboxic conditions this is consistent with the low sr concentrations for d2 36 4 8 ppm and d3 38 7 9 ppm 18o values of dolomitizing fluids for d2 2 1 to 8 1 vsmow and d3 6 to 8 1 vsmow coupled with fe contents of d2 1684 1096 ppm and d3 1783 7 618 ppm as well as the respective mn d2 131 2 50 and d3 197 5 55 ppm concentrations ree and shale normalized reesn values of catoche carbonates indicate enrichment in rare earth element ree composition of the earliest calcite c1 relative to those of arenig seawater whereas the reesn profiles of the dolomite generations mimic that of calcite c1 the ce ce ce sn and la la la pr pr sn anomalies of the catoche dolomites are consistent with precipitation in equilibrium with source fluids in slightly oxic to suboxic conditions whereas eu eu eu cn anomalies suggest similar source fluids for d2 and d3 results of fluid inclusion gas analysis are consistent with petrographic features and geochemical compositions and support the exclusion of magmatic fluids during dolomitization visual estimates of porosity from thin sections indicate four porous 4 12 horizons vugs and intercrystalline pores are two types of porosity associated with the dolomites with the latter being the dominant type and associated mainly with dolomite d2

trace elements and environmental significance of messinian gypsum deposits the nijar basin southeastern spain abstract the messinian evaporites in nijar basin southeastern spain are composed of coarse crystalline yesares selenites and feos laminated fine crystalline gypsum these primary yesares selenites feos gypsum and secondary vein gypsum were analyzed for trace elements na mg and sr in order to understand gypsum origin trace element concentrations from the three types of gypsum differ significantly the consistency of the yesares data with natural marine and modeled marine results suggests that yesares selenites were deposited from marine dominated environments within the entire yesares formation or within one single gypsum bed sr mg and na concentrations increase upward while crystal size decreases probably indicating an increase of brine concentration as yesares selenites were accumulating the sr na and mg concentrations from the feos gypsum are partially overlapped with but also significantly higher than those of the yesares selenites these feos data are inconsistent with natural marine and modeled marine data one interpretation for the inconsistency is that diagenetic alteration occurred to primary marine feos gypsum an alternative scenario is that the feos gypsum was deposited from mixed nonmarine fluids with marine brine during the late messinian the latter interpretation is consistent with the stratigraphic sedimentary and o s and sr isotopic data

martian aeolian features and deposits comparisons with general circulation model results the development of a general circulation model gcm of mars atmosphere allows questions to be addressed concerning the relationships between near surface winds and the distribution of wind related features and deposits predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks yardangs and rock abundance on the surface the occurrence and orientation of bright streaks are well accounted for by the gcm results suggest that bright streaks form during southern hemisphere summer by hadley cell circulation in which dust is raised in the southern hemisphere carried northward at high altitudes then deposited in the wake of craters and other topographic obstacles by the descending hadley cell the reduction in the number of bright streaks southward from 30 n is interpreted to reflect the depletion of dust by near surface winds blowing to the south although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by gcm simulations a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season southern hemisphere summer yardang orientations do not match the gcm simulations for any season their orientation is attributed to either structural control in the rocks such as joint patterns or to a change in wind patterns from the time when the yardangs formed the global distribution of rocks on the surface is correlated well with predicted wind stress particularly during dust storm season the rocky areas are sites of strong winds suggesting that fine material is swept away by the wind leaving rocks and coarser material behind

a comparative study of daytime thermally induced upslope flow on mars and earth abstract several characteristics of thermally induced mesoscale upslope flow on mars and its comparison with that on earth were investigated using both analytical and numerical model approaches the conclusions obtained from the analytical and the numerical evaluations for mars are generally in agreement the main conclusions are i the intensity of the martian summer daytime upslope flow with a moderate slope reaches nearly 10 m s 1 and its depth is about 5 km ii the longwave radiation flux divergence heating within the lower boundary layer of mars has a nonnegligible contribution to the intensity of the upslope flows and iii on mars the values of upslope wind speed are typically about 2 5 times larger than on earth under similar conditions the depth of the daytime upslope flow and the air temperature increase near the surface are 3 to 4 times larger the vertical eddy exchange coefficient for heat and momentum is about 10 times larger on mars

a comparison of methods used to estimate the height of sand dunes on mars the collection of morphometric data on small scale landforms from other planetary bodies is difficult we assess four methods that can be used to estimate the height of aeolian dunes on mars these are 1 stereography 2 slip face length 3 profiling photoclinometry and 4 mars orbiter laser altimeter mola results show that there is good agreement among the methods when conditions are ideal however limitations inherent to each method inhibited their accurate application to all sites collectively these techniques provide data on a range of morphometric parameters some of which were not previously available for dunes on mars they include dune height width length surface area volume and longitudinal and transverse profiles the utilization of these methods will facilitate a more accurate analysis of aeolian dunes on mars and enable comparison with dunes on other planetary surfaces

meteorological predictions for 2003 mars exploration rover high priority landing sites 1 the mars regional atmospheric modeling system is used to predict meteorological conditions that are likely to be encountered by the mars exploration rovers at several proposed landing sites during entry descent and landing seven areas five of which contain specific high priority landing ellipses are investigated hematite two sites isidis planitia elysium planitia two sites valles marineris and gusev crater the last two locations are in regions of extreme topography and the local and regional thermal circulations that result are equally extreme horizontal wind speeds near the floor of valles marineris exceed 50 ms 1 vertical velocities near the walls exceed 40 ms 1 and penetrate 10 km in altitude above the rim of the canyon thermal convection is suppressed within valles marineris by subsidence that forms in response to the upslope flows along the canyon walls wind magnitudes at gusev crater are approximately one third of those at the canyon but horizontal wind shear is greater deep convective thermals are noted at the relatively flat hematite site where 10 ms 1 updrafts rising to heights of 5 km are not uncommon during the midafternoon linearly organized convective updrafts superimposed on upslope circulations dominate over most of isidis planitia hexagonal and linearly organized convection predominates at elysium planitia afternoon circulations at all sites pose some risk significant risk in some cases to entry descent and landing most of the atmospheric hazards are not evident in current observational data and general circulation model simulations and can only be ascertained through mesoscale modeling of the region

periodicities in natural remanent magnetization and palaeoclimatic records detected by walsh spectra the time series consisting of nonsinusoidal natural remanent magnetization nrm and palaeoclimatic variations for the past two million years have been spectrally examined by using a new walsh transform technique the results show statistically significant periodicities at 95 confidence level of approximately 92 000 years 43 000 years and 21 000 years in the ensemble spectra of the nrm intensity mineralogic variations these nrm periodicities are remarkably close to the well known milankovitch cycles the ensemble spectra of palaeoclimatic records reveal only 41 000 years statistically significant 95 periodicity corresponding to the obliquity cycle the study suggests that nrm variations in deep sea sediments probably are more sensitive recorders of palaeoclimatic memory than the oxygen isotope variations

gravity wave drag in three dimensional atmospheric models of mars gravity waves are disturbances whose restoring force is buoyancy in the atmosphere they are made possible by the variation of potential temperature with height they can be excited by various mechanisms including flow over orography the momentum carried by these disturbances can exert significant drag forces on the mean flow in the terrestrial mesosphere one parameterization of this effect the lindzen gravity wave drag scheme is inserted into two simplified general circulation models gcms of the martian atmosphere and its effects are described the influence of large amplitude planetary scale topography on wave breaking altitudes is discussed we show that above 60 km in altitude gravity wave drag dominates the momentum balance of the martian atmosphere on the largest scales this indirectly alters the thermal state of the atmosphere through the thermal wind relation model winds at this level are consistent with other simpler studies as well as with earth based spectroscopic observations below 60 km the effects of planetary wave mean flow interaction as well as heating associated with hadley circulation descent are significant in determining the wind strength eddy diffusion coefficients derived from the lindzen parameterization above 50 km are consistent with values implied from chemical modeling of the martian middle atmosphere as well as with simpler models of gravity wave drag

selection of the mars exploration rover landing sites 1 the selection of meridiani planum and gusev crater as the mars exploration rover landing sites took over 2 years involved broad participation of the science community via four open workshops and narrowed an initial 155 potential sites 80 300 30 km to four finalists based on science and safety engineering constraints important to the selection included 1 latitude 10 n 15 s for maximum solar power 2 elevation less than 1 3 km for sufficient atmosphere to slow the lander 3 low horizontal winds shear and turbulence in the last few kilometers to minimize horizontal velocity 4 low 10 m scale slopes to reduce airbag spin up and bounce 5 moderate rock abundance to reduce abrasion or strokeout of the airbags and 6 a radar reflective load bearing and trafficable surface safe for landing and roving that is not dominated by fine grained dust the evaluation of sites utilized existing as well as targeted orbital information acquired from the mars global surveyor and mars odyssey three of the final four landing sites show strong evidence for surface processes involving water and appear capable of addressing the science objectives of the missions which are to determine the aqueous climatic and geologic history of sites on mars where conditions may have been favorable to the preservation of evidence of possible prebiotic or biotic processes the evaluation of science criteria placed meridiani and gusev as the highest priority sites the evaluation of the three most critical safety criteria 10 m scale slopes rocks and winds and landing simulation results indicated that meridiani and elysium planitia are the safest sites followed by gusev and isidis planitia

simulation of surface meteorology at the pathfinder and vl1 sites using a mars mesoscale model 1 the fifth generation penn state ncar mesoscale model mm5 has been adapted to study circulations in the martian atmosphere the nasa ames mars general circulation model gcm provides initial and boundary conditions the meteorology of this mars mm5 the osu mmm5 is compared with pathfinder and viking lander 1 vl1 data for late northern summer the mmm5 uses an equator crossing semiglobal polar stereographic mother domain significantly reducing the boundary reflections inherent in martian mesoscale simulations using two way nests simultaneous simulations of two regions are performed 1 chryse planitia mars pathfinder mpf vl1 and 2 the central chasmas of valles marineris simulations are hydrostatic and dry the mmm5 uses the same atmospheric radiation package as the gcm but a much enhanced near surface vertical resolution and a different planetary boundary layer pbl scheme model topography thermal inertia and surface albedo maps have all been developed using the most recent data from the mars global surveyor mgs mars orbiter laser altimeter mola and thermal emission spectrometer tes experiments the diurnal cycles of surface air temperature surface pressure and surface wind all show improvement in comparison with the gcm for certain regions the local surface pressure tidal amplitudes are strongly dependent on the resolution of the model and or the topography vl1 and mpf are in such a region the diurnal cycles of wind are complex and for many locations the near surface winds are dominated by slope flows of multiple scales comparison with data indicates that resolving these slope flows is very important for simulating the diurnal wind cycle at specific locations these slope flows dramatically influence the diurnal surface pressure cycle

periodicities of palaeomagnetic intensity and palaeoclimatic variations a walsh spectral approach abstract the walsh power spectral technique has been applied to the non sinusoidal palaeoclimatic thegloborotalia menardii climatic curve and palaeomagnetic intensity variation records of the last 1 2 myr the analysis reveals in the case of palaeomagnetic variations statistically significant peaks at 90 confidence level centered around 150 60 and 24 kyr the palaeoclimatic spectrum however indicates only two significant peaks of 60 and 24 kyr the identical periodicities in both the phenomena may suggest a causal link between the geomagnetic intensity variations and climatic changes

western boundary currents in the martian atmosphere numerical simulations and observational evidence western boundary currents hereafter wbcs are an intensification of meridional fluid flow along the eastward facing flank of a boundary they occur in the earth s oceans the best known instance being the gulf stream and in the terrestrial atmosphere an example of which is the east african jet we have investigated wbcs in numerical simulations of the martian atmosphere where they occur in the presence of large longitudinal topographical gradients combined with the effect we suggest that wbcs have already been simulated by other martian atmospheric models although not identified as such the intensity of these currents is dependent on basic model parameters notably surface drag we show that for physically reasonable values of drag frictional forces dominate the wbcs behavior the requirement of zero net cross equatorial time mean mass flow produces a return flow in simulations with relatively low surface drag which acts in opposition to the tharsis wbc we also show that the intense flow associated with wbcs advects potential vorticity across the equator although the presence of strong radiative damping inhibits low level inertial instabilities that might result from this slope winds are found to have a profound effect on wbc structure especially where they have a component parallel to the jet in these cases slope winds can cancel out or reinforce wbcs depending on their direction enhanced low level winds associated with wbcs may be a factor that influences the locations of dust storm generation the high vertical shear associated with wbcs may also play a role in the maintenance and subsequent decay of these dust storms some observational evidence may exist for wbcs in the form of the alignment of bright depositional dust streaks wave clouds and in wind measurements taken during the parachute descent phase of viking lander 1 through the planetary boundary layer

depositional sequences and correlation of middle to late miocene carbonate complexes las negras and nijar areas southeastern spain during serravallian through messinian time marine carbonates flanked topographic highs that rimmed neogene basins in the western mediterranean middle to upper miocene carbonate strata in the las negras and nijar areas southeastern spain are 50 150 m thick and display 50 200 m of shelf to basin relief over 1 2 km detailed studies in those areas document the effects of relative sea level change on sedimentation biotic composition and reef development we identify three previously unrecognized regionally correlatable depositional sequences ds1 ds2 ds3 that occur between the underlying basement and the overlying terminal carbonate complex the lower depositional sequences ds1 ds2 are mostly normal marine shelf ramp carbonates deposited on the flanks of basement highs the basal part of ds2 locally contains some megabreccia reef blocks composed of tarbellastraea and porites these blocks are the first evidence of reef growth in the area and represent a previously unrecognized period of reef development prior to the fringing reef development the reef blocks probably formed as upslope patch reefs that were eroded and transported to distal slope locations the upper sequence ds3 is characterized by clinoform strata of a porites dominated fringing reef complex that prograded basinward in a downstepping style with successively younger reefs forming in a topographically lower and more basinward position as a result of a net sea level drop regional correlation of miocene shallow marine strata between basins in spain and elsewhere in the western mediterranean is complicated because basins were semi isolated from adjacent basins making physical correlation impossible in addition age definitive biostratigraphic markers are poorly preserved in most of the miocene shallow water strata basinal sediments that are more easily dated by microfossils do not typically interfinger with the shallow marine strata in outcrop even where datable microfossils are found resolution of dating is poor our studies in the las negras and nijar areas illustrate the usefulness of integrating sedimentological geometric and biotic data with locally derived relative sea level accommodation space curves for correlation the relative sea level curves for each area show remarkable similarities in shape and magnitude of sea level changes these curves indicate several relative sea level fluctuations during miocene carbonate deposition prior to the major sea level drop at the end of ds3 deposition that culminated in the exposure of the basin margin deposits and the deposition of evaporites in basinal areas during the messinian the depositional sequences in the las negras and nijar areas may correlate with depositional sequences of similar age throughout the southern cabo de gata area in mallorca some 600 km to the northeast and possibly in other mediterranean locations the widespread occurrence and possible correlation of the depositional sequences suggest regional processes such as eustacy or tectonism for their formation the integration of sedimentological palaeontological and sequence stratigraphic studies and the construction of relative sea level accommodation space curves may help in the interpretation of depositional histories of shallow marine carbonate complexes and correlation of these strata between isolated areas other dating methods in addition to microfossil dating may allow for better age determination of the sequences and aid in identifying the importance of eustacy and tectonism in sequence development

late miocene events in the mediterranean as recorded by carbonate evaporice relations the messinian stage in the mediterranean region is known mainly because of a major evaporitic event whose causes and global implications are still under discussion correlations between basinal evaporite bearing series and marginal carbonate platforms allow for improvement of the classical depostional models especially concerning the eustatic control of the environmental changes in the mediterranean these changes were controlled by the interplay of aperiodic and periodic factors 1 tectonics related to the relative motions of the african and eurasian plates and resultant linear increase in the basin restriction 2 sea level fluctuations that alternately aggravated the restriction or allowed marine replenishment and 3 climatic fluctuations that controlled the level of the mediterranean during stages of isolation the messinian sedimentary succession reflects a typical sequence of progressive isolation marine marls yields laminites yields transitional deposits yields evaporites yields lacustrine deposits the first stage of the so called salinity crisis was characterized by a mediterranean lowstand that resulted in erosion of former platforms and deposition of the lower evaporites during the next stage sea level rose tb3 3 cycle high enough to temporarily replenish the basin cyclic upper evaporites with development of stromatolite rich deposits finally the uppermost messinian freshwater to brackish lacustrine deposits reflect both themore cessation of sea water input maximum tectonic isolation low sea level and freshwater input related to increasing runoff less

atmospheric entry profiles from the mars exploration rovers spirit and opportunity abstract accelerometer measurements made by spirit and opportunity during their entries through the martian atmosphere are reported vertical profiles of atmospheric density pressure and temperature with sub km vertical resolution were obtained using these data between 10 and 100 km spirit s temperature profile is 10 k warmer than opportunity s between 20 and 80 km unlike all other martian entry profiles spirit s temperature profile does not contain any large amplitude long wavelength oscillations and is nearly isothermal below 30 km opportunity s temperature profile contains a strong inversion between 8 and 12 km a moderate dust storm which occurred on mars shortly before these two atmospheric entries may account for some of the differences between the two profiles the poorly known angle of attack and unknown wind velocity may cause the temperature profiles to contain errors of tens of kelvin at 10 km but these errors would be an order of magnitude smaller above 30 km on broad scales the two profiles are consistent with mars global surveyor thermal emission spectrometer tes pressure temperature profiles differences exist on smaller scales particularly associated with the near isothermal portion of spirit s profile and the temperature inversion in opportunity s profile

the mars limited area model and simulations of atmospheric circulations for the phoenix landing area and season of operation 1 the mars limited area model mlam has been used to simulate martian northern polar atmospheric circulation phenomena during the planned season of the phoenix lander touching down on the surface ls 76 initial and boundary conditions are from thermal emission spectrometer observations assimilated via the united kingdom mars general circulation model the higher resolution north pole centric nestings grid lengths about 17 30 km and 8 5 15 km respectively resolve phenomena such as shallow mesoscale katabatic drainage flows spiraling out of the cold polar dome strong valley winds out of chasma borealis and diurnal slope winds embedded on the easterly basic flow e g at phoenix landing area d there conditions appear to be mild for mars and baroclinic activity is low low level jets with wind speeds exceeding 20 m s are however possible but they are most likely nocturnal and would hence not endanger the early afternoon landing of phoenix dust lifting is predicted for strong wind areas near the landing area b where baroclinic activity appears to be high and in the general area of the landing area d primarily east of it

anhydrite cements after dolomitization of shallow marine silurian carbonates of the gascoyne platform southern carnarvon basin western australia abstract carbonates and evaporites in the dirk hartog group were deposited in subtidal peritidal and shallow marine evaporitic mudflat environments across the gascoyne platform within the southern carnarvon basin western australia the carbonates are composed of ooids peloids and minor bioclastic fragments with early cements they have been extensively dolomitized and replaced in part by late anhydrite sparry cements four types of dolomite which range from early to burial types are identified incorporating re equilibration or re crystallization from basin brines accordingly they exhibit distinctive petrographic features and isotopic signatures of carbon and oxygen evaporites deposited are present as discrete beds and displacive nodules in carbonate and siliciclastic beds and show 34scdt values and 87sr 86sr ratios indicative of variable marine and non marine conditions late dissolution of evaporites has produced satin spar gypsum veins in the shallowest section of the platform whereas blocky and sparry anhydrite cements and void fillings formed deeper within the platform dissolution of the evaporites and formation of anhydrite cements post date dolomitization

holocene dolomitization of calcium carbonate sediments from the coastal sabkhas of abu dhabi u a e a stable isotope study secondary dolomitization of holocene calcium carbonate sediments occurs beneath the coastal sabkhas of abu dhabi u a e a stable isotope study of the sabhka sediments and brines indicates that the

a multi year survey of dynamics near the surface in the northern hemisphere of mars short period baroclinic waves and dust storms abstract baroclinic waves figure prominently in the dynamics of the northern hemisphere of mars and extensive observations by the viking landers and two atmospheric sounders on mars global surveyor have revealed many of their basic properties however previous investigations considered these data sets individually so that their cumulative value is not fully appreciated we have re examined these data to extract new information about the dynamics near the surface at mid to high northern latitudes by applying the same method of spectral analysis to each type of observation we derive a uniform multi year characterization of basic elements of martian weather this survey documents the time evolution of baroclinic waves among modes with different periods and zonal wave numbers we devote particular attention to a recurring wave 3 mode which is distinguished by its capacity to initiate regional dust storms in the topographic basins of the northern hemisphere our results include a detailed case study that shows how the intermittence of this mode and the strong zonal modulation of its amplitude influence the timing and location of these distinctive flushing dust storms more generally we find that the properties of the wave 3 mode are largely the same whenever it appears and that its intermittence plays an important role in the annual dust cycle

the meteorology of gale crater as determined from rover environmental monitoring station observations and numerical modeling part ii interpretation abstract numerical modeling results from the mars regional atmospheric modeling system are used to interpret the landed meteorological data from the rover environmental monitoring station onboard the mars science laboratory rover curiosity in order to characterize seasonal changes throughout the martian year simulations are conducted at ls 0 90 180 and 270 two additional simulations at ls 225 and 315 are explored to better understand the unique meteorological setting centered on ls 270 the synergistic combination of model and observations reveals a complex meteorological environment within the crater seasonal planetary circulations the thermal tide slope flows along the topographic dichotomy mesoscale waves slope flows along the crater slopes and mt sharp and turbulent motions all interact in nonlinear ways to produce the observed weather ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong flushing northerly flow and large amplitude breaking mountain waves at other seasons the air in the crater is more isolated from the surrounding environment the potential impact of the partially isolated crater air mass on the dust water noncondensable and methane cycles is also considered in contrast to previous studies the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations with contributions of less than 25 to the diurnal amplitude from the crater circulation itself the crater circulation is shown to induce a suppressed boundary layer

the martian slope winds and the nocturnal pbl jet abstract the summertime martian pbl diurnal wind variation slope winds and the nocturnal low level jets were studied using prandtl s theory a mesoscale numerical model and viking lander observations during moderate prevailing large scale flow nocturnal jets were simulated that were rather similar to those on earth they were mainly caused by inertial oscillation after sunset with some contribution from the slope wind effects over sloping regions which are very common in mars during weak large scale flow shallow nocturnal drainage flows with strong vertical shear developed over the cold martian slopes at middle and high latitudes these katabatic winds tended to turn to flow along the slope by dawn due to the coriolis force for sufficiently steep slopes near surface drainage winds could reach considerable speeds in contrast the typical afternoon upslope winds were vertically homogeneous up to 2 3 km and weak only 1 3 m s 1 in magnitude even over relatively steep large scale slopes

barchan dune asymmetry observations from mars and earth barchan dune asymmetry refers to the extension of one barchan limb downwind it is a common dune form on earth and also occurs on mars and titan a new classification of barchan limbs is presented where three types of limb morphology are identified linear kinked and beaded these along with other dune scale morphological signatures are used to identify three of the causes of barchan asymmetry on mars bi directional winds dune collision and the influence of inclined topography the potential for specific dune asymmetric morphologies to indicate aspects of the formative wind regime on planetary surfaces is shown for example the placement of dune limbs can indicate the general direction and relative strength of formative oblique winds an extreme barchan limb length may indicate a long duration oblique wind a kinked limb may be evidence of the passage of a storm beaded limbs may represent surface wave instabilities caused by an increase in wind energy parallel to the dune a preliminary application of these signatures finds evidence for bi modal winds on mars however these and other morphological signatures of wind direction and relative strength should be applied to planetary landforms with caution as more than one process e g bi modal winds and collision may be operating together or sequentially on the dunefield in addition analysis should be undertaken at the dunefield scale and not on individual dunes finally morphological data should be acquired from similar scale dunes within a dunefield in addition to bi modal wind regimes on mars the frequent parallel alignment of the extended barchan limb to the dune suggests that dune collision is also an important cause of asymmetry on mars some of the more complex dunefield patterns result from a combination of dune collision limb extension and merging with downwind dunes dune asymmetric form does not inhibit dune migration in the namib desert or on mars data from the namib suggest that dune migration rates are similar for symmetric and asymmetric dunes further modeling and field studies are needed to refine our understanding of the potential range of limb and dune morphologies that can result from specific asymmetry causes

late pleistocene mixing zone dolomitization southeastern barbados west indies field geochemical and petrographic data for late pleistocene dolomites from southeastern barbados suggest that the dolomite precipitated in the zone of mixing between a coastal meteoric phreatic lens and normal marine waters the dolomite is localized in packstones and wackestones from the algalamphistegina fore reef calcarenite facies stable isotopic evidence suggests that meteoric water dominated the diagenetic fluids responsible for dolomitization carbon isotopes in pure dolomite phases average about 15 0 pdb this light carbon is attributed to the influence of soil gas co2 and precludes substantial mixing with seawater a narrow range of oxygen isotopic compositions coupled with a wide range of carbon compositions attest to the meteoric diagenetic overprint dolomitization likely occurred with as little as a five per cent admixture of seawater strontium compositions of the dolomites indicate probable replacement dolomitization of original unstable mineralogy the dolomite is characterized by low sodium values low concentrations of divalent manganese and iron suggest oxidizing conditions at the time of dolomitization a sequence of petrographic features suggests a progression of diagenetic fluids from more marine to more meteoric early marine diagenesis was followed by replacement dolomitization of skeletal grains and matrix limpid euhedral dolomite cements precipitated in primary intra and interparticle porosity subsequent to replacement dolomitization as waters became progressively less saline dolomite cements alternated with thin bands of syntaxial calcite cement the final diagenetic phase precipitated was a blocky calcite spar cement representing diagenesis in a fresh water lens this sequence of diagenetic features arose as the result of a single fall in eustatic sea level following deposition a stratigraphic eustatic diagenetic model constrains both the timing and rate of dolomitization in southeastern barbados dolomitization initiated as sea level began to fall immediately following the oxygen isotope stage 7 3 high stand some 216 000 yr bp due to the rapidity of late pleistocene glacio eustasy dolomitization locally complete is constrained to have occurred within about 5000 yr

the composition and origin of brines during the messinian desiccation event in the meditterranean basin as deduced from concentrations of ions coprecipitated with gypsum and anhydrite abstract gypsum and anhydrite from the upper miocene messinian evaporites of the mediterranean basin were analysed for their coprecipitated ion compositions the concentrations of mg na k sr and cl in gypsum and anhydrite samples from dsdp leg 42a sites 372 374 and 376 and from boreholes yafo 1 ashdod 2 talme yafe 3 and afiq 1 from the coastal plain of israel were used to calculate the composition of the brines from which these calcium sulfate minerals were deposited or in which they have undergone recrystallization or phase transformation results reveal basic differences between the eastern central and western mediterranean basins during the last stage of the messinian salinity event the western mediterranean and the ionian basin were characterized by marine brines during most of the second stage of the salinity event upper evaporite member during this period the eastern mediterranean basins were fed with brines of continental origin these brines are characterized by high ca concentrations relative to seawater brines one core from the eastern mediterranean yafo 1 indicated that anhydrite was deposited along the continental margin of the eastern mediterranean from brines of marine composition which evolved into carich continental brines following a marine regression

s and o so 4 isotopes simultaneous modeling and environmental significance of the nijar messinian gypsum spain abstract the messinian evaporites in nijar basin southeastern spain consist of coarse grained primary selenites and laminated fine grained gypsums these gypsums which are similar to those deposited in other mediterranean messinian basins have rather variable 34 s and 18 o so 4 21 to 24 for 34 s 10 to 17 for 18 o that are generally greater than the normal tertiary marine values 21 22 for 34 s and 13 for 18 o moreover the variation of 18 o so 4 is larger than that of 34 s continental input and reservoir effect did not play important roles for these isotope variations because these factors should have resulted in lower 34 s and 18 o so 4 than the normal marine values redox reactions of sulfur species in brine should have been responsible for the isotope variations to interpret the variable 34 s and 18 o so 4 we quantitatively modeled 34 s and 18 o so 4 of dissolved sulfate during redox reactions in two marine evaporative settings in sediment pores in a shallow water pan and in a free brine column in a deep water basin modeled 34 s and 18 o of dissolved sulfate during reduction of sulfate yield small variations especially for o isotopes in a shallow water pan however modeled 34 s and 18 o of dissolved sulfate during reduction and reoxidation cycling processes in a deep water basin show a progressive increase of up to 10 for both 34 s and 18 o so 4 above their normal marine values importantly the modeled pathways for the deep water basin setting are consistent with the nijar data whereas those for pore waters in shallow water pans are a poor fit to the nijar data the modeled results consistent with trace elements sr isotope data and selenite fabrics suggest that these yesares selenites have formed in deep marine brines the modeling results also demonstrate that 18 o so 4 can have larger variation than 34 s because the incorporation of water oxygen and probably dissolved free oxygen increases 18 o of the reoxidized sulfate whereas reoxidation of sulfide to sulfate decreases the total 34 s so 4 the modeled results could provide important geological implications for isotope and environment interpretations for ancient evaporites for example redox reactions of sulfur species during sulfate precipitation could modify normal marine 34 s and 18 o so 4 more efficiently than freshwater contributions and reservoir effects therefore to establish 34 s and 18 o so 4 age curves redox processes for ancient evaporites should be considered

a walsh spectral comparison of oxygen δ18o and carbon isotope δ13c variations of the pleistocene bore hole eureka 67 135 from the gulf of mexico and their orbital significance abstract a new spectral analysis known as walsh spectral analysis of the oxygen 18o and carbon 13c isotopic variations during the pleistocene the past 1 7 m y reveals periodicities in milankovitch frequency bands besides three main spectral cycles eccentricity obliquity and precession the walsh spectra also reveals additional periodicity in a range of 57 000 60 000 years in case of oxygen isotopic variations only that remarkably corresponds to combined effect of obliquity and precession as suggested by berger walsh spectra of both records also exhibits significant power in a range of 29 000 34 000 years throughout the pleistocene this periodicity is also similar to the one predicted in orbital variations 29 000 31 000 years and lies in obliquity bands precessional signal during the early part of the pleistocene 0 85 1 7 m y seems to be weak however eccentricity and obliquity signals dominate throughout the pleistocene walsh spectra of both phenomena exhibits a general similarity in their spectral structures suggesting a common link in view of appearance of some unusual periodicities in walsh spectra and their striking resemblance with orbital cycles the present result further lends support to the astronomical theory of climatic change

modification of fracture porosity by multiphase vein mineralization in an oligocene nontropical carbonate reservoir taranaki basin new zealand the nontropical oligocene carbonate rich tikorangi formation is an important oil producer in the taranaki basin new zealand hydrocarbons are hosted and produced from mineralized natural fracture systems petrographic trace element stable isotope 18o and 13c and fluid inclusion data have enabled a complex sequence of eight paragenetic events to be determined the tikorangi formation host rock was cemented by low mg calcite event 1 during burial diagenesis from temperatures of 27c corresponding to 0 5 km burial and continued until 37c 1 km burial depth producing tight pressure dissolved fabrics with essentially no porosity and permeability the host rock was partially dolomitized 5 50 event 2 by ca and fe rich dolomite rhombohedra at burial depths and temperatures of 1 0 1 5 km and 35 50c without secondary porosity development subsequent brittle fracturing formed by neogene compression event 3 is constrained to a period following lithification and dolomitization but before precipitation of first generation vein calcite event 4 this initial ferroan low mg vein calcite formed after a period of burial from fe rich meteorically modified fluids at temperatures of about 50 60c and 1 4 1 9 km burial depth baroque dolomite formed event 5 following a period of mg enriched basinal fluid input precursory to hydrocarbon emplacement per se the dolomite formed mainly as a primary cement but also as a calcite replacement at temperatures following further burial to 2 2 5 km and temperatures of 65 80c formation of celestite and quartzine phases event 6 coincided with or marginally postdated dolomite at similar depths and temperatures to event 6 and formed as both replacements and cements second generation ferroan vein calcite formed event 7 at cooler temperatures 53 65c perhaps resulting from the introduction of cooler meteoric fluids from upsection the presence of petroleum fluid inclusions in the second generation calcite suggests precursory hydrocarbon bearing fluids have migrated along with aqueous fluids from about 10 ma with hydrocarbon emplacement event 8 occurring in the last 6 m y following a period of rapid late miocene burial an improved understanding of the paragenesis of the tikorangi formation may assist in hydrocarbon production from its reservoirs

geology of the melas chasma landing site for the mars exploration rover mission 1 the melas chasma landing site was considered a high priority site for the mars exploration rover mer mission because of the opportunity to land on and study potential layered sedimentary deposits though no longer considered a candidate site because of safety concerns the site remains a scientifically interesting area that provides insight into the geologic history of valles marineris within the landing ellipse are dunes landslide material and unusual blocky deposits the blocky deposits are composed of rounded blocks some of which have meter scale layering and they show evidence of ductile deformation including bending and distortion of coherent blocks around each other the morphologic characteristics of the blocks are unique and they appear to have no terrestrial analogue however the gross morphology of these blocky deposits and their superposition on adjacent wallrock is consistent with the blocks having been transported downslope given the existence of other large mass failures in the area we propose the blocky deposits may also have originated from mass movement events the size of the blocks coupled with the distances they traveled indicates high mobility the distances the blocks were transported and their rounded irregular shapes suggest either water in the source material or deposition in a subaqueous environment the source for the main blocky deposit inside the landing ellipse is considered to be the wallrock to the south while the other two blocky deposits have source regions along the northern canyon walls the southern wallrock of melas chasma contains numerous valleys not seen elsewhere in valles marineris the identification of valley networks along the southern wallrock suggests that a source of water existed below the surface of the plateau and produced the valleys after intersecting the edge of the exposed canyon walls

analysis of atmospheric mesoscale models for entry descent and landing 1 each mars exploration rover mer is sensitive to the martian winds encountered near the surface during the entry descent and landing edl process these winds are strongly influenced by local mesoscale conditions in the absence of suitable wind observations wind fields predicted by martian mesoscale atmospheric models have been analyzed to guide landing site selection in order to encompass the available models and render them useful to the edl engineering team a series of statistical techniques was applied to the model results these analyses cover the high priority landing sites during the expected landing times 1200 1500 lt the number of sites studied is limited by the computational and analysis cost of the mesoscale models the statistical measures concentrate on the effective mean wind the wind as seen by the landing system and on the vertical structure of the horizontal winds both aspects are potentially hazardous to the mer landing system in addition a number of individual wind profiles from the mesoscale model were processed into a form that can be used directly by the edl monte carlo simulations the statistical analysis indicates that the meridiani planum and elysium landing sites are probably safe the gusev crater and isidis basin sites may be safe but further analysis by the edl engineers will be necessary to quantify the actual risk finally the winds at the melas chasma landing site and presumably other valles marineris landing sites are dangerous while the statistical parameters selected for these studies were primarily of engineering and safety interest the techniques are potentially useful for more general scientific analyses one interesting result of the current analysis is that the depth of the convective boundary layer and thus the resulting energy density appears to be primarily driven by the existence of a well organized mesoscale or regional circulation primarily driven by large scale topographic features at mars

lithofacies and water body record of messinian evaporites in nijar basin se spain abstract the depositional lithofacies and fabrics of messinian evaporites have been studied to evaluate the palaeodepth of water body in nijar basin se spain the nijar messinian strata consist of three formations abad marls yesares evaporites and feos rocks gypsum deposits dominate the yesares formation and the basal feos formation six gypsum lithofacies have been identified including coarse twinned selenite grass like selenite hemiradial to radial selenite turbidite selenite in the yesares formation and gypsum conglomerate laminated gypsum and hemiradial to radial selenite in the feos formation the size of yesares selenites decreases upward while carbonate content and trace element abundance increase in each selenite bed and the whole formation suggesting a shallowing up sequence these gypsum lithofacies were deposited in subaqueous environments commonly at 10 30 m and occasionally up to 100 m or deeper for the turbiditic selenites based on the interpretations of gypsum fabrics marl intervals basin configuration and geochemistry the sea level of nijar basin experienced two major drops with a magnitude of 40 m before and after the deposition of yesares evaporites however the basin was never desiccated during the evaporite deposition and the change of sea level for the alternative deposition of gypsum beds and marl intervals was commonly around 50 80 m probably resulting from the glacio eustacy fluctuations feos gypsum reflects another evaporative event and is correlated to the upper evaporite while the yesares selenite is correlated to the lower evaporite based on the interpretations of lithofacies geochemistry and sealevel change as seawater in nijar basin was continuously supplied by the central mediterranean basins and remained in subaqueous conditions during the messinian salinity crisis therefore the desiccation theory needs to be reexamined

massive dolomitization of a late miocene carbonate platform a case of mixed evaporative brines with meteoric water nijar spain late miocene platform carbonates from nijar spain have been extensively dolomitized limestones are present in the most landward parts of the platform in stratigraphically lower units and topographically highest outcrops suggesting that dolomitizing fluids were derived from the adjacent nijar basin the dolomite crystals range from 10 to 100 m existing as both replacements and cements na cl and so4 concentrations in the dolomites range from 200 to 1700 p p m 250 650 p p m and 600 7000 p p m respectively comparable with other tertiary and modern brine dolomite values and also overlapping values from mixing zone dolomites sr concentrations range between 50 and 300 p p m and the molar sr ca ratios of dolomitizing fluids are estimated to range between 7 seawater brine to freshwater ratios the 18o and 13c of the dolomites range from 1 0 to 4 2 pdb and 4 0 to 2 0 pdb respectively 87sr 86sr values 0 70899 0 70928 of the dolomites range from late miocene seawater to values greater than modern seawater mixtures of freshwater with seawater and evaporative brines probably precipitated the nijar dolomites modelled covariations of molar sr ca vs 18o and na ca vs 18o from these mixtures are consistent with those of the proposed nijar dolomitizing fluids complete or partial dolomite recrystallization is ruled out by well preserved cl zoning nonstoichiometry and quantitative water rock interaction modelling of covariations of na vs sr and 18o vs 13c the possibility of multiple dolomitization events induced by evaporative brines seawater and freshwater respectively is consistent with mineral mineral mixing modelling the basin derived dolomitizing brines probably mixed with freshwater in the nijar basin or mixed with fresh groundwater in the platform and were genetically related either to deposition of the yesares gypsum or the feos gypsum dolomitization occurred during either the middle messinian or the early upper messinian nijar dolomitization models may be applicable to dolomitization of other late miocene platform carbonates of the western mediterranean moreover the nijar models may offer an analogue for more ancient evaporite absent platform carbonates fringing evaporite basins

constraints on mars recent equatorial wind regimes from layered deposits and comparison with general circulation model results aeolian modification has been a fundamental surface process on mars throughout the amazonian orientations of aeolian features such as bedforms and yardangs are controlled by the prevailing wind regime during the feature s formation therefore observation of recently formed bedform orientations provides a way to probe mars recent wind regime and constrain test general circulation models gcms we collect statistical distributions of transverse bedform and yardang azimuths at nine sites on mars and compare measured feature orientations to those predicted by using vector wind field output from the marswrf gcm we focus on layered deposits because their erodible nature makes them applicable to determination of mars modern wind regime our methods of mapping from the long term wind field to predicted feature orientations include consideration of wind stress thresholds for sand movement to occur sand flux equations and the direction of maximum gross bedform normal transport we find that all methods examined typically agree with each other to within 15 though there are some exceptions using high order wind stress weightings with multi directional annual wind fields generally use of higher wind stress thresholds produces improved matches to bedform orientations comparison of multiple yardang orientations to annually variable wind fields is accomplished by inspection of directional maxima in modelled wind vector frequency distributions yardangs match well to model predictions and sub populations in close proximity to each other are shown to match individual directional maxima in gcm output for a single site implying that topographic effects may produce very localised unidirectional wind fields unresolved by the gcm

towards a high resolution global deep sea chronology for the last 750 000 years abstract variations in the ratio of 18 o 16 o as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume hence these variations provide a set of global time lines in deep sea sediments it is likely that the timing of major changes in oxygen isotope values is strongly influenced if not controlled by variations in the geometry of the earth s orbit since the variation of orbital parameters can be accurately calculated the opportunity exists for transforming this orbital chronology into a geological chronology through careful correlation of oxygen isotope records in a set of deep sea cores from the sub antarctic south atlantic and equatorial pacific we have assembled a composite isotopic section spanning the last 750 000 years with an average sedimentation rate of 2 3 cm 1000 years a new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300 000 years to the entire 750 000 year record previously identified difficulties in phase locking precession with the filtered isotopic signal between 365 000 and 465 000 years b p have been resolved with the recognition that precessional variations have an average period of 19 000 years and not 23 000 years during this interval since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record we believe that it presents the most accurate chronology yet developed for deep sea sediments with this new age model providing the time control power spectral analyses of south atlantic and sub antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of 100 000 41 000 and 23 000 years

shallow burial dolomite cement a major component of many ancient sucrosic dolomites dolomite cement is a significant and widespread component of phanerozoic sucrosic dolomites cements in dolomites that were never deeply buried are limpid have planar faces non saddle forms often distinct zonation in cathodoluminescence and form syntaxial overgrowths on crystals facing pores five samples of sucrosic dolomites interpreted as having had mostly limemudstone or wackestone precursors in four carbonate aquifers provide insights into the abundance of planar cements in sucrosic dolomites such cement comprises 11 to 45 32 mean of peritidal to sub tidal dolomites on an outcrop in the edwards aquifer early cretaceous of central texas 19 to 33 25 mean of ramp dolomites in the hawthorn group oligomiocene and 50 to 70 in shelf dolomites of the avon park formation eocene in the upper floridan aquifer of sub surface peninsular florida 18 to 45 32 mean of sub tidal shelf dolomites in quarry sections of the burlington keokuk formation early mississippian in south eastern iowa and 18 to 76 50 mean in shallow cores and outcrops of outer shelf dolomites from the gambier limestone oligo miocene of south australia backstripping the cement phases revealed by cathodoluminescence colour photomicrographs documents the effects of cements on textural coarsening pore space reduction induration and general maturation of these dolomites most pre holocene dolomites are multiphase crystalline rocks composed of i seed crystals or cores ii crystal cortices that concentrically enlarged the cores and iii free space syntaxial precipitates of limpid cement around the crystals remaining caco3 grains and micrite can be replaced by dolomite but typically they are dissolved between stages ii and iii creating systems of intercrystal and mouldic pores typical of sucrosic dolomites networks of cement overgrowths aided by water filled pore systems under hydrostatic to lithostatic pressure are judged to slow or prevent compaction in sucrosic dolomites it can be argued that cortex growth involves both replacement of caco3 particles and microcementation of their interparticle pores this interpretation and the abundance of cements in so many dolomites would obviate the controversy over the volumetrics of replacement dolomitization limpid planar and syntaxial dolomite cements of early diagenetic origin are interpreted to have precipitated from clear pore waters at low temperatures 30 to 35 c and shallow burial depths 100 m in water saturated networks of dolomite silt and sand cements in many dolomites in island and continental aquifer systems appear to result from event driven processes related to sea level highstands cementation events can follow replacement

evidence for red sea surface circulation from oxygen isotopes of modern surface waters and planktonic foraminiferal tests hydrographic data and oxygen isotopic analyses performed on surface waters and planktonic foraminiferal tests collected during early summer from two succeeding years 1984 1985 throughout the red sea reveal two different hydrographic regimes in 1984 the summer normal situation prevailed where surface waters from the red sea flowed out into the gulf of aden while in 1985 a reversed inflow current occurred the higher temperatures and salinities observed in 1985 indicate high evaporation rates and increased aridity in the northern red sea and caused this inflow of indian ocean surface water which origins from the active upwelling region in the arabian sea lower salinities and lower oxygen isotopes were observed up to 18 n the occurrence of globorotalia menardii during 1985 with its surprisingly constant isotope values up to the gulf of suez indicates northward flowing surface currents for the entire red sea isotope values from neogloboquadrina dutertrei 1985 indicate subsurface shell formation to about 50 m water depth oxygen isotope analysis on globigerinoides ruber and globigerinoides trilobus from the 1984 and 1985 tracks suggests that both species calcify in isotopic equilibrium with the surrounding water in the gulf of aden and in the northern red sea while an offset from equilibrium values of up to 0 4 is found in the red sea occurrences of g menardii in red sea sediments may be useful as a tool for detecting unusual hydrographic situations preserved in the sediment record when subsurface water was brought to the surface by upwelling in the arabian sea and flowed into the red sea as this process is triggered by high evaporation rates in the northern red sea region the appearance of this species in red sea sediments may also indicate periods with extreme arid conditions

the messinian of the nijar basin se spain sedimentation depositional environments and paleogeographic evolution abstract the reconstruction of the depositional events related to the messinian salinity crisis msc of the mediterranean is generally hampered by an incomplete stratal record in the circum mediterranean basins the sediments of the northern part of the nijar basin however provide an excellent and continuous record of late messinian sediments because features of severe erosion are lacking especially the successions of the deeper part of the basin had sufficient accommodation space to warrant ongoing deposition and may thus serve as a testing ground for existing hypotheses regarding the msc conformable contacts with the overlying pliocene and good correlation possibilities with the adjacent astronomically dated messinian of the sorbas basin provide the necessary age constraints the main body of evaporites in the nijar basin yesares formation has been affected by local dissolution and erosion prior to deposition of the latest messinian lago mare facies pelitic float breccias show textures indicating flowage and or mass transport and include slumped and slided stratal packets due to foundering of the mixed evaporitic clastic margin increased runoff of meteoric waters probably played an important role as these packet slides are perfectly sealed by the hyposaline lago mare strata field observations show that marginal sediments commonly classified as the terminal carbonate complex tcc are a lateral equivalent of the basinal yesares evaporites the latest messinian deposits feos formation are characterized by a sedimentary cyclicity related to fluctuating base levels consisting of chalky marly laminitic strata alternating with continental coarser clastic intervals despite considerable w e facies changes and indications for discrete tectonic events a persistent sequential pattern of eight lago mare cycles is present which are interpreted as precession controlled variations in regional climate instead of one major desiccation event in the latest messinian the repeatedly fluctuating water levels of the lago mare episode may have been the cause of the widespread vigorous erosion and canyon cutting in the lower evaporites abrupt non erosional contacts with the normal marine pliocene take place above the continental interval of the last lago mare cycle indicating that flooding took place during a period of lowered water levels the paleogeographic configuration of the nijar sorbas and vera basins has changed considerably during the messinian separation of the formerly interconnected basins is thought to have started in the late yesares times by tectonic uplift of the basement complexes in the latest messinian of the nijar basin two different coarse clastic supply areas can be distinguished which point to the partial emergence of the sierra cabrera and the cabo de gata block and activity of the sierra alhamilla and carboneras faults concerning the overall regional tectonic activity tectonics were probably also instrumental for the restoration of the atlantic gateway in the basal pliocene

remote sensing of surface pressure on mars with the mars express omega spectrometer 2 meteorological maps 1 surface pressure measurements help to achieve a better understanding of the main dynamical phenomena occurring in the atmosphere of a planet the use of the mars express omega visible and near ir imaging spectrometer allows us to tentatively perform an unprecedented remote sensing measurement of martian surface pressure omega reflectances in the co2 absorption band at 2 m are used to retrieve a hydrostatic estimation of surface pressure see companion paper by forget et al 2007 with a precision sufficient to draw maps of this field and thus analyze meteorological events in the martian atmosphere prior to any meteorological analysis omega observations have to pass quality controls on insolation and albedo conditions atmosphere dust opacity and occurrence of water ice clouds and frosts for the selected observations registration shifts with the mola reference are corrected sea level surface pressure reduction is then carried out in order to remove the topographical component of the surface pressure field three main phenomena are observed in the resulting omega surface pressure maps horizontal pressure gradients atmospheric oscillations and pressure perturbations in the vicinity of topographical obstacles the observed pressure oscillations are identified as possible signatures of phenomena such as inertia gravity waves or convective rolls the pressure perturbations detected around the martian hills and craters may be the signatures of complex interactions between an incoming flow and topographical obstacles highly idealized mesoscale simulations using the wrf model enable a preliminary study of these complex interactions but more realistic mesoscale simulations are necessary the maps provide valuable insights for future synoptic and mesoscale modeling which will in turn help in the interpretation of observations

dolomitization of the late cretaceous paleocene platform carbonates golkoy ordu eastern pontides ne turkey abstract late cretaceous paleocene agillar formation in the eastern pontide zone ne turkey is composed of shallow marine platform carbonates that were buried until uplift in late paleocene time the formation which is represented by 100 m thick reefal limestones around golkoy is completely dolomitized on the basis of petrographic and geochemical features four different replacive and cement dolomite phases are present the replacive dolomites which are cut by low amplitude stylolites include 1 fine crystalline planar s dolomite rd1 and 2 coarsely crystalline planar s e dolomite rd2 two types of dolomite cements were developed in minor amounts 1 a coarse dolomite cement cd1 that mostly fills molds vugs and fractures in rd1 dolomites and 2 rim dolomite cement cd2 that commonly develops on the space facing surfaces of rd2 dolomite the replacive dolomites are nearly stoichiometric ca 49 51 mg 48 50 and have 18 o values of 3 5 to 1 6 vpdb 13 c values of 1 1 to 0 8 vpdb and 87 sr 86 sr ratios of 0 707104 to 707458 sr na mn and fe concentrations of replacive dolomites are 102 171 ppm bdl 371 ppm 244 9941 ppm and 2643 8951 ppm respectively petrographic and geochemical data indicate that the replacive dolomites were formed prior to chemical compaction at shallow to intermediate burial depths from late cretaceous paleocene seawater and or seawater slightly modified by water rock interaction process and then recrystallized by meteoric waters at increasing burial depths and temperatures compared with replacement dolomites cd1 dolomites yield lower 18 o values 4 9 to 5 3 vpdb similar 13 c values 1 2 to 0 5 vpdb and higher 87 sr 86 sr ratios 0 707660 0 707609 the cd1 dolomites overlie the low amplitude stylolites and have homogenization temperatures between 94 and 112 c indicating that they were deposited from basinal brines although replacive dolomites and dolomite cements have similar na bdl 413 ppm mn 259 6990 ppm and fe 2184 6690 ppm concentrations the cements have lower sr contents 63 114 ppm like replacive dolomites cd1 dolomite is nearly stoichiometric ca 49 50 mg 47 49 but cd2 dolomite is slightly ca rich ca 51 52 mg 47 48 the cd2 dolomite is overlain by coarsely crystalline mosaic calcite cement indicates that diagenetic fluids eventually evolved to undersaturation with respect to dolomite and oversaturation with respect to calcite

a new model to simulate the martian mesoscale and microscale atmospheric circulation validation and first results 1 the laboratoire de meteorologie dynamique lmd mesoscale model is a new versatile simulator of the martian atmosphere and environment at horizontal scales ranging from hundreds of kilometers to tens of meters the model combines the national centers for environmental prediction ncep national center for atmospheric research ncar fully compressible nonhydrostatic advanced research weather research and forecasting arw wrf dynamical core adapted to mars with the lmd general circulation model gcm comprehensive set of physical parameterizations for the martian dust co2 water and photochemistry cycles since lmd gcm large scale simulations are also used to drive the mesoscale model at the boundaries of the chosen domain of interest a high level of downscaling consistency is reached to define the initial state and the atmosphere at the domain boundaries a specific hybrid vertical interpolation from the coarse resolution gcm fields to the high resolution mesoscale domain is used to ensure the stability and the physical relevancy of the simulations used in synoptic scale mode with a cyclic domain wrapped around the planet the mesoscale model correctly replicates the main large scale thermal structure and the zonally propagating waves the model diagnostics of the near surface pressure wind and temperature daily cycles in chryse planitia are in accordance with the viking and pathfinder measurements afternoon gustiness at the respective landing sites is adequately accounted for on the condition that convective adjustment is turned off in the mesoscale simulations on the rims of valles marineris intense daytime anabatic 30 m s 1 and nighttime katabatic 40 m s 1 winds are predicted within the canyon corridors topographical channeling can amplify the wind a few kilometers above the ground especially during the night through large eddy simulations in gusev crater the model describes the mixing layer growth during the afternoon and the associated dynamics convective motions overlying gravity waves and dust devil like vortices modeled temperature profiles are in satisfactory agreement with the miniature thermal emission spectrometer mini tes measurements the ability of the model to transport tracers at regional scales is exemplified by the model s prediction for the altitude of the tharsis topographical water ice clouds in the afternoon finally a nighttime warm ring at the base of olympus mons is identified in the simulations resulting from adiabatic warming by the intense downslope winds along the flanks of the volcano the surface temperature enhancement reaches 20 k throughout the night such a phenomenon may have adversely affected the thermal inertia derivations in the region

geometry palaeoenvironments and relative sea level accommodation space changes in the messinian murdjadjo carbonate platform oran western algeria consequences abstract the messinian carbonate platform of the djebel murdjadjo western algeria is composed of six sedimentary units arranged in generally aggradational progradational sequences commencing at the major tortono messinian transgression and terminating at the onset of the salinity crisis palinspastic reconstruction combined with microfacies analysis has allowed recognition of inner platform to outer platform environments and provides a new interpretation for platform building with respect to relative sea level accommodation space changes following the deposition of the bioclastic limestones of the first transgressive unit the upper red algae limestones a reef complex and a part of the terminal complex were successively deposited during stillstands these three episodes were each separated by decametre amplitude rises in relative sea level accommodation space no major sea level drop appears to have been associated with the deposition of messinian evaporites

dolomitization of the lower ordovician aguathuna formation carbonates port au port peninsula western newfoundland canada implications for a hydrocarbon reservoir the lower ordovician aguathuna formation 100 m thick is formed of shallow marine carbonates which constitute the uppermost part of the st george group of western newfoundland sedimentation wa

initial results from radio occultation measurements with mars global surveyor a series of radio occultation experiments conducted with mars global surveyor in early 1998 has yielded 88 vertical profiles of the neutral atmosphere the measurements cover latitudes of 29 n to 64 s and local times from 0600 through midnight to 1800 during early summer in the southern hemisphere ls 264 308 retrieved profiles of pressure and temperature versus radius and geopotential extend from the surface to the 10 pa pressure level near surface uncertainties in temperature and pressure are about 1 k and 2 pa respectively far smaller than in previous radio occultation measurements at mars the profiles resolve the radiative convective boundary layer adjacent to the surface and also reveal gravity waves particularly at northern and equatorial latitudes which appear to be breaking in some cases distinctive meridional gradients of pressure and temperature indicate the presence of a low altitude westerly jet at latitudes of 15 30 s at southern summer solstice this jet appears in predictions of general circulation models in connection with the strong seasonal cross equatorial hadley circulation the pressure gradient at 2 km altitude implies a wind speed of 33 m s 1 stronger than predicted which may help explain the occurrence of numerous local dust storms within this latitude band in late southern spring these measurements also characterize the response of the atmosphere to stationary thermal forcing at midsouthern latitudes where high terrain south of tharsis and low terrain in hellas planitia produce large zonal temperature variations in the lowest scale height above the surface pressure measured at constant geopotential decreases at an average rate of 0 13 per degree ls due primarily to condensation of co2 at the north pole

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less