the effects of soluble salts on the threshold shear velocity of fine sand wind tunnel tests were carried out to investigate the effects of two soluble salts nacl and kci on the threshold shear velocity of a well sorted fine sand a sensitive laser monitoring system was used to detect initial grain motion during the tests results indicate that even small amounts of soluble salt can significantly increase the threshold velocity of the sand because of cement like bonds formed between grains that tend to hold individual particles in place however with increasing concentration the salt crystal growth causes the initially smooth sand surface to develop an irregular frothy texture which also directly affects the threshold shear velocity this is indicated by increased scatter of data on the threshold shear velocity surface salt concentration plots for both nacl and kcl although data scatter is evident significant exponential relationships do exist between threshold shear velocity and surface salt concentration in each case

facies and beddding sequences in shelf storm deposited carbonates fayetteville shale and pitkin limestone mississippian arkansas abstract the fayetteville shale miss is a black marine shale that was deposited on a southward deepening ramp in northern arkansas it is conformably overlain by skeletal oolitic grainstones of the pitkin limestone and together they form a shoaling upward succession of 1 deep muddy shelf 2 storm dominated muddy shelf and 3 ooid skeletal shoal and shoreface facies rhythmically bedded limestones of the upper fayetteville shale and some lower pitkin ooid grainstones are interpreted to be shelf storm deposits because of their stratigraphic position and bedding sequences upper fayetteville limestone beds are transitionally positioned between cephalopod bearing black shales deep muddy shell underneath and cross bedded ooid grainstones shoal and shoreface above fayetteville and pitkin beds are similar to other reported shelf storm deposits in that they contain hummocky cross stratification hcs and unidirectional climbing ripple cross stratification thought to have been laid down by combined flows six principal types of bedding sequences were noted in order of increasing water depth and or distance from the inferred shore 1 cross bedded and planar laminated beds with some keystone vugs beach 2 graded units of coarse skeletal ooid grainstone shoreface 3 planar laminated and hummocky cross stratified limestones lower shoreface 4 hummocky cross stratified limestones and thin shales storm dominated muddy shelf 5 fine grainstones with parallel laminae in lower half followed above by climbing ripple cross stratification storm dominated muddy shelf and 6 structureless lime mudstones and black shale deep muddy shelf reconstruction of the ancient shelf suggests that it sloped southward at 0 08 to 0 14 and the water depth at 30 km estimated width of storm dominated shell was 40 to 70 m the paleolatitudinal position of northern arkansas 5 15 s indicates that strong tropical storms or hurricanes rather than intense winter storms were responsible for eroding carbonate sediment from lower shoreface environments and depositing it as much as 30 km offshore in the muddy shelf

regional scale flows in mountainous terrain part i a numerical and observational comparison abstract this study uses observed data and a numerical simulation to examine the generation of thermally driven flows across the colorado mountain barrier on meso to meso scales the observations were collected from remote surface observing systems at exposed mountaintop locations throughout the state of colorado over the summers of 1984 88 as part of the rocky mountain peaks experiment rompex the data show the development of a recurrent circulation system across the colorado mountain barrier operating on a diurnal timescale from the observations the basic structure of the flow system appears as a daytime inflow toward the highest terrain and a nocturnal outflow away from it however when examined in detail the flow system exhibits more unusual behavior especially west of the barrier crest here winds in the early evening are occasionally observed to onset abruptly from an easterly direction generally counter to the upper level winds observations from rompex for 26 august 1985 are used

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

upper devonian mississippian stratigraphic framework of the arkoma basin and distribution of potential source rock facies in the woodford chattanooga and fayetteville caney shale gas systems wireline logs were used to document the stratigraphic framework of upper devonian mississippian strata in the arkoma basin and maps of high gamma ray hgr log response were used to analyze the spatial distribution of potential source rocks in the woodford chattanooga and fayetteville caney shale gas systems the woodford chattanooga shale is a transgressive deposit that accumulated on an arid continental margin influenced by marine upwelling and minimal sediment influx a broad hgr depocenter along the southwestern margin of the basin includes two areas of higher accommodation containing the thickest hgr concentrations basin wide patterns of hgr likely reflect broad tectonic influence on accommodation the proportion of chert in the formation increases eastward and southward likely reflecting latitudinal and bathymetric influence on the accumulation of siliceous ooze the lower mississippian burlington sequence which lies between the two shale gas systems comprises carbonate ramp and distal shale deposits proximal ramp facies form an apron around the southern flank of the ozark uplift and grade radially basinward into distal facies an upper mississippian succession in the east includes lowstand deposits of the batesville delta which onlap the relict burlington ramp basinwide the succession includes the transgressive fayetteville caney shale overlain by regressive deposits of the proximal pitkin limestone and distal upper fayetteville arkansas and false caney oklahoma shale the hgr shale is concentrated in an area of intermediate accommodation on the western margin of the mississippi embayment and just basinward of the pitkin limestone pinchout in arkansas and in an area of relatively high accommodation in oklahoma

pressure perturbations and upslope flow over a heated isolated mountain abstract surface and upper air data collected as part of the cumulus photogrammetric in situ and doppler observations cupido experiment during the 2006 monsoon season around the santa catalina mountains in southeast arizona are used to study the diurnal variation of the mountain scale surface convergence and its thermal forcing the thermal forcing is examined in terms of a horizontal pressure gradient force which is derived assuming hydrostatic balance the mountain is 30 km in diameter 2 km high and relatively isolated the environment is characterized by weak winds a deep convective boundary layer in the afternoon and sufficient low level moisture for orographic cumulus convection on most days the katabatic divergent surface flow at night and anabatic convergent flow during the day are in phase with the diurnal variation of the horizontal pressure gradient force which points toward the mountain during the day and away from the mountain at night the daytime pressure deficit over the mo

aeolian sand drift from the intertidal zone on a temperate beach potential and actual rates this paper compares the amount of sand that is potentially moved into a coastal dune system from a beach using estimates based solely on the wind force with actual measured amounts the actual sand inputs are determined by measuring sand level changes each month over a period of eighteen months along a 1760 m section of foredune on braunton burrows southwest england the calculation procedure used to estimate the potential rates of sand drift is based on the capacity of the wind force to transport sand using a published transport equation white 1979 the results show that the actual movement rates are markedly smaller than the potential rates for all months except in the summer meteorological variables and the watertable level in the adjacent dune system are used in an empirically derived regression equation in an attempt to explain the large discrepancy between the potential and actual movement rates the resulting corrected potential movement rates are a closer estimate to the actual rates but there remains much unexplained variance

the climate archive dune sedimentary record of annual wind intensity active dunes contain an unread high resolution archive of past wind strength variations in the grain size spectrum of an active dune through time are compared with historical time series of wind speed annually averaged sediment derived wind intensity and instrumental records of wind speed show a correlation as high as 0 75 the potential of eolian dunes to gain long term data series of wind intensity in areas and for time periods lacking an instrumental record is demonstrated by reconstructing 20th century wind intensity variations in the southern north sea area the approach can be used in both recent and fossil dune systems potential applications include the validation of climate models the reconstruction of supraregional wind systems and the monitoring of future shifts in the climate system

rotational reflectance of dispersed vitrinite from the arkoma basin abstract rotational reflectance of dispersed vitrinite provides superior documentation of thermal maturity and a capability for interpreting relative timing between thermal and kinematic events in arkoma basin strata characterized by vitrinite reflectances up to 5 rotational reflectance rrot is a more precise and less ambiguous index of thermal maturity than maximum r max minimum r min and random rran reflectance vitrinite reflectance anisotropy becomes sufficiently large to be measurable using a microscope equipped with an automated rotating polarizer at 2 rrot and increases following a power function with increasing thermal maturity rotational reflectance data can be used to infer the shape of the vitrinite reflectance indicating surface i e indicatrix and in turn to enhance interpretations of the timing between thermal maxima and compressional tectonic events data from three wells in the arkoma basin ouachita frontal thrust belt are used as examples the absence of offsets in measured rrot across thrust faults combined with a predominance of uniaxial vitrinite in the thrust faulted part of the section suggest thermal maximum postdated thrust faulting in the western ouachita frontal thrust belt of oklahoma in contrast the general absence of offsets in measured rrot across thrust faults combined with a predominance of biaxial vitrinite in the thrust faulted part of the section suggest that the thermal maximum was coeval with thrust faulting in the eastern ouachita frontal thrust belt of arkansas the presence of biaxial vitrinite in an allochthonous section and uniaxial vitrinite in an underlying autochthonous section suggests that the thermal maximum was coeval with listric thrust faulting in the central arkoma basin of oklahoma and that rotational reflectance data can be used as a strain indicator to detect subtle decollement zones

effects of time dependent moisture content of surface sediments on aeolian transport rates across a beach wildwood new jersey u s a a one day field investigation on an unvegetated backbeach documents the importance of surface sediment drying to aeolian transport surface sediments were well sorted fine sand moisture content of samples taken in the moist areas on the backbeach varied from 2 9 to 9 2 per cent lack of dry sediment inhibited transport prior to 08 50 by 09 10 conspicuous streamers of dry sand moved across the moist surface barchan shaped bedforms 30 to 40 mm high and composed of dry sand moisture content 0 10 per cent formed where sand streamers converged the surface composed of dry sand increased from 5 per cent of the area of the backbeach at 09 50 to 90 per cent by 12 50 mean wind speeds were beetween 5 6 and 8 6 m s 1 at 6 m above the backbeach corresponding shear velocities were always above the entrainment threshold for dry sand and below the threshold for the moist sand on the backbeach measured rates of sand trapped by vertical cylindrical traps increased during the day relative to calculated rates the measured rate of sand trapped on the moist foreshore was higher than the rate trapped on the backbeach during the same interval indicating that the moist foreshore moisture content 18 per cent was an efficient transport surface for sediment delivered from the dry portion of the beach upwind measured rates of sand trapped show no clear relationship to shear velocities unless time dependent surface moisture content is considered results document conditions that describe transport across moist surfaces in terms of four stages including 1 entrainment of moist sediment from a moist surface 2 in situ drying of surface grains from a moist surface followed by transport across the surface 3 entrainment and transport of dry sediment from bedforms that have accumulated on the moist surface and 4 entrainment of sand from a dry upwind source and transport across a moist downwind surface 1997 john wiley sons ltd

diurnal circulation of the bolivian altiplano part ii theoretical and model investigations abstract the first step in the evolution of the diurnal circulation of grand plateaus is the matutinal buildup of inflow through mountain passes connecting the lowlands with the plateau proper maximum inward transport is attained in the afternoon corresponding observations at the bolivian altiplano are described in the first part of this paper here both a linear model and the fifth generation pennsylvania state university ncar mesoscale model mm5 are used to better understand the dynamics of this process first discussed is the solution to the linear sea breeze problem where a heated fluid layer is restricted to the half plane x 0 rapidly moving barotropic modes lead to surface pressure fall in the heated half plane and to pressure rise for x 0 slow baroclinic modes describe the horizontally expanding inflow toward the heated layer near the ground with return flow aloft this basic structure of the response carries over to more complicated topographies where a heated plateau with vertical side

temporal and spatial variabilities in the surface moisture content of a fine grained beach abstract this study examined spatial and temporal variations in the surface moisture content of a fine grained beach at padre island texas usa surface moisture measurements were collected on a 27 24 m grid that extended from the dune toe to the upper foreshore the grid was surveyed at 2 to 4 h intervals for two tidal cycles generating 17 maps of the spatial distribution of surface moisture simultaneous measurements of air temperature and humidity wind speed and direction tidal elevation and water table elevation were used to interpret observed changes in surface moisture it was found that the spatial distribution of surface moisture was broadly characterized by a cross shore gradient of high to low content moving landward from the swash zone the distribution of surface moisture was conceptualized in terms of three zones saturated 25 intermediate or transitional 5 25 and dry

the dynamism of salt crust patterns on playas playas are common in arid environments and can be major sources of mineral dust that can influence global climate these landforms typically form crusts that limit evaporation and dust emission modify surface erosivity and erodibility and can lead to over prediction or underprediction of 1 dust emission potential and 2 water and heat fluxes in energybalance modeling through terrestrial laser scanning measurements of part of the makgadikgadi pans of botswana a southern hemisphere playa that emits significant amounts of dust we show that over weeks months and a year the shapes of these surfaces change considerably ridge thrusting of 30 mm week and can switch among continuous ridged and degraded patterns ridged pattern development changes the measured aerodynamic roughness of the surface as much as 3 mm week the dynamic nature of these crusted surfaces must be accounted for in dust entrainment and moisture balance formulae to improve regional and global climate models

petrographic and geochemical characterization of organic rich mississippian black shales in the north of spain vegamian formation cantabrian zone abstract black shales 1 60 m thick with minor cherts radiolarites and phosphate nodules of mississippian age middle upper tournaisian vegamian formation occur in the fold and thrust belt of the cantabrian zone n spain at the base of the carboniferous succession which is infilling the variscan foreland basin the vegamian formation was accumulated in a similar sedimentary and paleogeographic context to the upper devonian carboniferous black shales of the appalachian arkoma fort worth western canada and antler foreland basins north america and to the variscan foreland basin in belgium and germany five stratigraphic sections were investigated in the southern branch of the cantabrian zone corresponding to the shallower sectors of the passive margin of the variscan foreland basin in n spain where this stratigraphic unit reaches a thickness of generally the organic matter is dominated by bitumen found either as diffuse masses or concentrated in spaces and cavities often parallel to the bedding planes or filling voids within calcite veins and fractures generally the bitumen masses are homogeneous without secondary porosity but occasionally they show mosaic optical texture indicating thermal transformation anastomosing structures likely related to bituminite are also common and exhibit a large range of reflectances autochthonous organic matter algae bacteria is seen as scarce tasmanites and liptodetrinite whereas allochthonous components vitrinite inertinite are also scarce except in the olleros section the range of reflectances of vitrinite like particles is similar to that of bitumen but the identification is uncertain and therefore the reflectance of bitumen brr has been used for thermal maturity assessment a gaussian like distribution of bitumen reflectances was found for la brana section brr 0 70 whereas a bimodal distribution was observed in olleros brr 0 70 and vegamian sections brr 0 95 and large scatter of readings in millaro brr 1 55 the vitrinite reflectance equivalent estimated from aromatic compounds indicates that most of the existing correlations between vitrinite and bitumen reflectances underestimate the maturity of the lowest reflecting sections and overestimate it in the highest reflecting one ts toc ratios the geochemistry of organic matter and spectral gamma ray measurements suggest a normal marine to dysoxic environment of deposition with only local anoxia at the base of the vegamian formation

wind tunnel modelling of the influence of vegetation structure on saltation threshold the influence of vegetation structure on saltation threshold was investigated using uniformly spaced arrays of non erodible roughness elements on a bed of erodible sand in an wind tunnel structural variables tested using arrays of solid cylinders included element aspect ratio height diameter and lateral cover total frontal silhouette area per unit ground area in agreement with previous studies increase in saltation threshold above the value for bare sand was strongly related to lateral cover increasing aspect ratio from 0 25 to 4 tended to enhance the increase in saltation threshold at a given lateral cover an approximate fit to the results could be obtained using a relation proposed by raupach et al journal of geophysical research 1993 98d 3023 3029 porous elements were constructed as clusters of narrow vertically oriented cylinders model stems forming porous model plant bodies that were cylindrical in overall shape low porosity elements were found to be approximately 50 per cent more effective in increasing saltation threshold than either solid or high porosity elements the ratio of plant body frontal silhouette area based on overall dimensions to total stem frontal silhouette area was found to be a useful measure of plant body porosity for wind erosion studies some conventional measures of vegetation amount fail to account for changes in vegetation structural attributes that may strongly influence aeolian processes

the dynamic effects of moisture on the entrainment and transport of sand by wind abstract there is an increasing awareness of the influence of surface moisture on aeolian entrainment and transport of sediment existing wind tunnel studies have shown the impact of a limited range of moisture contents on entrainment thresholds but similar investigations are lacking in the field the research reported here investigated the influence of changes in surface moisture content on sand entrainment and transport on a meso tidal beach in anglesey north wales high frequency 1 hz wind velocities measured with hot wire anemometers were combined with grain impact data from a sensit monitor and mass flux measurements from a standard sand trap surface and near surface moisture contents were assessed gravimetrically from surface sand scrapes and also directly by using a thetaprobe critical threshold values for entrainment were specified using a modified form of the time fraction equivalence method stout j e zobeck t m 1996a establishing the threshold condition for soil movement in wind eroding fields proceedings of the international conference on air pollution from agricultural operations mwps c 3 kansas city 7 9 february 1996 pp 65 71 results indicate a time dependent change in dominant control of the sand transport system from moisture to wind speed dependent upon the moisture content of the surface sediment this interchange between controlling parameters on both entrainment and transport was very sensitive to prevailing moisture conditions and took place over a period of minutes to hours under conditions experienced in the experiments presented here the critical moisture threshold for sediment entrainment was determined to be between 4 and 6 higher than the 1 4 specified in previous wind tunnel experiments furthermore a moisture content of nearly 2 where moisture was adhered to transported sediment appeared to have little or no impact on the rate of sand flux

diurnal circulation of the bolivian altiplano part i observations in july and august 2003 a field campaign was conducted to explore the diurnal circulation of the bolivian altiplano vertical soundings by remote controlled aircraft yielded profiles of temperature pressure and humidity at six passes and in a valley pilot balloon observations provided wind profiles two permanent stations collected additional data typically inflow toward the altiplano commences a few hours after sunrise at about the time when the stable nocturnal layer near the ground is transformed by the solar heating into an almost neutrally stratified convective boundary layer the depth of the inflow layer is comparable to but normally less than that of this boundary layer there are indications of return flow aloft the inflow continues at least until sunset moisture is imported at the passes leading to the yungas in the east strong upvalley flows were found in the valley of the rio de la paz which connects the wide canyon of la paz with the tropical lowlands to the east inflow was absent at one of the passes despite favorable synoptic conditions cases of synoptically forced flows are presented as well where the diurnal signal is difficult to separate a simple flow scheme is presented that fits the observations reasonably well

a simple method to estimate threshold friction velocity of wind erosion in the field 1 this study provides a fast and easy to apply method to estimate threshold friction velocity tfv of wind erosion in the field wind tunnel experiments and a variety of ground measurements including air gun pocket penetrometer torvane and roughness chain were conducted in moab utah and cross validated in the mojave desert california patterns between tfv and ground measurements were examined to identify the optimum method for estimating tfv the results show that tfvs were best predicted using the air gun and penetrometer measurements in the moab sites this empirical method however systematically underestimated tfvs in the mojave desert sites further analysis showed that tfvs in the mojave sites can be satisfactorily estimated with a correction for rock cover which is presumably the main cause of the underestimation of tfvs the proposed method may be also applied to estimate tfvs in environments where other non erodible elements such as postharvest residuals are found

hotspot origin of the mississippi embayment and its possible impact on contemporary seismicity abstract previous authors have related the late cretaceous early tertiary subsidence of the mississippi embayment to the opening of the gulf of mexico but the gulf opened earlier in triassic jurassic time we offer an alternative hypothesis that development of the embayment was coeval with the passage of the mississippi valley graben system over the bermuda hotspot about 90 ma several lines of evidence of significant uplift of the embayment axis accompanying mid cretaceous magmatism and prior to late cretaceous subsidence support this proposal first reactivation of the pascola arch in the northern embayment is recorded by flanking deposits of basal upper cretaceous gravel second beneath a regional mid cretaceous unconformity subcrops of jurassic and early cretaceous strata define a pronounced southwest plunging arch in the southern embayment this arch is collinear with an arch revealed in paleozoic rocks after restoration to mid cretaceous structural geometries third a deep weathering profile on mid cretaceous alkalic plutons along the western embayment margin is nonconformably overlain by paleocene sediments and rapid mid cretaceous cooling of these intrusions has been interpreted from apatite fission tracks moreover exploratory holes along the embayment axis encountered similar weathered alkalic intrusions nonconformably overlain by basal upper cretaceous strata fourth there was an anomalous influx of clastic sediment into the northern gulf of mexico during mid cretaceous time and subsequent clastic facies patterns suggest the mississippi river drainage began to enter the gulf in the late cretaceous passage of the mississippi valley graben over the bermuda hotspot during elevated hotspot activity of cretaceous time may have significantly weakened the previously rifted lithosphere rifted continental margin at charleston south carolina also passed over this hotspot in latest cretaceous time similarly the st lawrence rift system passed over the great meteor hotspot during the cretaceous it is important to note that these rift systems are the principal loci of strong seismicity in eastern north america and thus weakening by increased cretaceous hotspot activity may be an important common factor for these seismic rift zones

kerogen maturation and incipient graphitization of hydrocarbon source rocks in the arkoma basin oklahoma and arkansas a combined petrographic and raman spectrometric study dispersed kerogen of the woodford chattanooga and atoka formations from the subsurface of the arkoma basin show a wide range of thermal maturities 0 38 to 6 1 ro indicating thermal conditions ranging from diagenesis to incipient rock metamorphism raman spectral analysis reveals systematic changes of both the first and second order spectrum with increasing thermal maturity these changes include a pronounced increase in the d o peak height ratio accompanied by a narrowing of the d peak a gradual decrease in the d o peak width ratio and a shift of both peaks toward higher wave numbers second order raman peaks though less intensive also show systematic peak shifting as a function of ro these empirical results underscore the high potential of raman spectrometry as a fast and reliable geothermometer of mature to supermature hydrocarbon source rocks and as an indicator of thermal maturity levels within the anchizone

the initiation of particle movement by wind when air blows across the surface of dry loose sand a critical shear velocity fluid threshold ut must be achieved to initiate motion however since most natural sediments consist of a range of grain sizes fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size shape sorting and packing of the surface sediment in order to investigate the initiation of particle movement by wind a series of wind tunnel tests was carried out on a range of pre screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics a sensitive laser monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep rolling or in saltation bouncing or hopping downwind as velocity continues to rise larger or less exposed grains may also be moved by fluid drag on striking the surface saltating grains impart momentum to stationary grains this impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure as a result there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities the fluid threshold range and setting in motion a rapidly increasing number of grains results of the tests showed that the progression from fluid to dynamic threshold based on grain movement can be characterized by a power function the coefficients of which are directly related to the mean size and sorting characteristics of the sediment

three dimensional seismic interpretation from the triangle zone of the frontal ouachita mountains and arkoma basin pittsburg county oklahoma analysis of 28 5 km 2 of three dimensional 3 d seismic reflection data from the triangle zone of the ouachita fold and thrust belt and the foreland arkoma basin reveals structural details not recognized previously in conventional two dimensional 2 d seismic data the data indicate that the frontal kiowa syncline in the arkoma basin has been passively uplifted by blind thrusting at the morrowan wapanucka limestone level and that smaller wavelength folds are produced by thrusting at shallower levels in the atoka formation faulting at deeper levels in the hunton and arbuckle groups has been traditionally interpreted as normal but our analysis of this data set indicates that in this area normal faults were reactivated during the ouachita orogeny as reverse faults and the changes in fault separation can be followed along strike these faults show the same trend as the overlying thrusts and are normal or have minor inversion where the overlying thrusts have small displacement these faults have been completely inverted where the overlying thrusts have more displacement suggesting a genetic relation between the wapanucka thrusts and the inversion of the hunton and arbuckle faults four reflections were chosen for analysis one reflection in the lower atoka formation two reflections repeated in the wapanucka limestone and a fourth reflection in the hunton group all of these surfaces exhibit the same geometry with the fold axes plunging to the southwest variations in bearing and plunge of fold axes in the wapanucka limestone can be directly correlated to changes in displacement and ramp height along strike the similarity between surface geometries suggests that the last deformation took place at deeper levels in the hunton and arbuckle groups and folded the overlying thrusts reactivation of atokan normal faults at deeper levels in the arkoma basin and ouachita subthrust play may be more widespread than previously recognized

thermal maturity of woodford shale gas and oil plays oklahoma usa abstract being a hydrocarbon source rock and having a brittle silica rich lithologic character makes the woodford shale late devonian to early mississippian an important oil and gas shale in oklahoma since 2004 woodford shale plays have expanded from producing primarily thermogenic methane in one geologic province to producing thermogenic methane condensate oil and biogenic methane in four geologic provinces at thermal maturities from mature 0 5 vitrinite reflectance ro to post mature 2 to 3 ro condensate is produced at a thermal maturity up to 1 67 ro oil is produced from naturally fractured silica rich shale biogenic methane is produced in shallow

geomorphology and drift potential of major aeolian sand deposits in egypt abstract aeolian sand deposits cover a significant area of the egyptian deserts they are mostly found in the western desert and northern sinai in order to understand the distribution pattern and forms of sand dunes in these dune fields it is crucial to analyze the wind regimes throughout the sandy deserts of the country therefore a set of wind data acquired from twelve meteorological stations were processed in order to determine the drift potential dp the resultant drift potential rdp and the resultant drift direction rdd of sand in each dune field the study showed that the significant aeolian sand deposits occur in low energy wind environments with the dominance of linear and transverse dunes regions of high energy wind environments occur in the south of the country and exhibit evidence of deflation rather than accumulation with the occurrence of migratory crescentic dunes analysis of the sand drift potentials and their directions help us to interpret the formation of major sand seas in egypt the pattern of sand drift potential direction suggests that the sands in these seas might be inherited from exogenous sources

the role of sound waves in sea breeze initiation the dynamics of the pressure distribution associated with the sea breeze circulation is investigated analysis of hourly observations of surface pressure reveals that on a typical sea breeze day large surface pressure falls are recorded very far inland using a linear numerical model we show that this can only be understood when sound waves are taken into account sound waves are excited when air in the boundary layer over land expands due to diabatic heating the numerical study reveals that vertically travelling sound waves induce a pressure increase through the entire atmosphere above the heated layer within a few minutes while horizontally travelling sound waves induce a surface pressure decrease over land and a surface pressure increase over sea with the resulting horizontal surface pressure gradient initiating the sea breeze because the signal travels inland at the speed of sound about 300 m s 1 points at a distance of more than 1000 km from the coast experience a surface pressure decrease within an hour after the initiation of diabatic heating over land the pressure decrease near the earth s surface over land as well as the pressure increase aloft is in accord with the observations at mountain stations and the analyses of the observed daytime surface pressure changes in summer over the continent and adjacent seas the implications of these findings for hydrostatic modelling of sea breezes are investigated it appears that after one hour the hydrostatic sea breeze is 10 stronger than the non hydrostatic sea breeze while the hydrostatic return current is about 20 weaker

a compositional classification for grain assemblages in fine grained sediments and sedimentary rocks reply abstract a tripartite compositional classification is proposed for sediments and sedimentary rocks that have grain assemblages with greater than 50 percent of a weight or volume of particles smaller than 62 5 m 4 phi tarl terrigenous argillaceous contains a grain assemblage dominated by more than 75 percent of particles of extrabasinal derivation including grains derived from continental weathering and also volcanogenic debris carl calcareous argillaceous contains less than 75 percent of particles of extrabasinal derivation debris and among its intrabasinal grains contains a preponderance of biogenic carbonate particles including carbonate aggregates sarl siliceous argillaceous contains less than 75 percent of particles of extrabasinal derivation and contains a preponderance of biogenic siliceous particles over carbonate grains these three classes of fine grained particulate sediments and rocks effectively separate materials that have distinct depositional settings and systematic contrasts in organic matter content and minor grain types in the subsurface the grain assemblages that define these classes follow contrasting and predictable diagenetic pathways that have significant implications for the evolution of bulk rock properties and thus assigning a fine grained rock to one of these classes is an important first step for predicting its economic and engineering qualities for purposes of description these three class names can be joined to modifier terms denoting rock texture more precise compositional divisions specific grain types of notable importance and diagenetic features

stratified flow over a mountain with a gap linear theory and numerical simulations linear theory and numerical simulations are used to investigate gap flows both gaps embedded in a long mountain ridge and gaps located between two isolated mountain peaks are considered the study mainly focuses on level gaps so as to isolate three dimensional effects from two dimensional gravity wave propagation special attention is given to qualitative differences between the linear and the nonlinear flow regimes the linear regime being defined by the absence of gravity wave breaking in the linear regime wind and pressure perturbations along a level gap axis are found to be qualitatively similar to those over a mountain ridge or peak but of lower amplitude and longer horizontal wavelength they are caused by vertically propagating gravity waves radiating from the mountain ridges peaks towards the gap axis and by low level confluence within the gap in the nonlinear regime however these two processes are of minor importance due to upstream blocking and low level wave breaking instead the pressure difference across the mountain ridge primarily drives the gap flow which tends to be decoupled from the flow over the adjacent ridge in contrast to the linear regime gap winds are as strong as or even stronger than the winds over the mountain ridge surface friction is found to reduce the near surface wind speed more strongly for mountain ridges than for gaps copyright 2002 royal meteorological society

determination of organic matter content of appalachian devonian shales from gamma ray logs the organic matter content of the devonian shale of the appalachian basin is important for assessing the natural gas resources of these rocks and patterns of organic matter distribution convey information on sedimentary processes and depositional environment in most of the western part of the appalachian basin the organic matter content of the devonian shale can be estimated from gamma ray wire line logs using the equation phgro ggrb ggr 1 378a where phgro is the organic matter content of the shale fractional volume ggr the gamma ray intensity api units ggrb the gamma ray intensity if no organic matter is present api units and a the slope of the crossplot of gamma ray intensity and formation density api units g cm3 the quantities a and ggrb vary regionally and are mapped using data from gamma ray and formation density wire line logs organic matter contents estimated using this equation are compared with organic matter contents determined from direct laboratory analyses of organic carbon for 74 intervals of varying thickness from 12 widely separated wells the organic matter content of these intervals ranges from near zero to about 20 by volume excluding the cleveland member of the ohio shale and the lower part of the olentangy shale the distribution of the differences between volume percent organic matter content determined from core samples and estimated from gamma ray logs has a mean of 0 44 and a standard deviation of 1 98 which indicates that the accuracy of the gamma ray method is adequate for most geologic applications the gamma ray intensity of the cleveland member of the ohio shale and the lower pa t of the olentangy shale is anomalously low compared to other devonian shales of similar richness so that organic matter content computed for each of these units from gamma ray logs is likely to be too low wire line methods for estimating organic matter content have the advantages of economy readily available sources of data and continuous sampling of the vertically heterogenous shale section the gamma ray log in particular is commonly run in the devonian shale its response characteristics are well known and the cumulative pool of gamma ray logs forms a large and geographically broad data base the quantitative computation of organic matter content from gamma ray logs should be of practical value in studies of the appalachian devonian shale the general approach described here may also be applicable to other formations with physical and geochemical characteristics similar to the appalachian devonian shale

petroleum reservoirs within a spiculite dominated depositional sequence cowley formation mississippian lower carboniferous south central kansas oil and gas reservoirs in the cowley formation upper osagean to lower meramecian are within a thick up to 400 ft 122 m section of spiculite dominated rocks derived from demosponges deposited in a low latitude setting these rocks are present in the subsurface for 325 mi 523 km along paleostrike in southern kansas and some adjoining states they represent a stratigraphically significant lithosome that markedly contrasts thin and areally restricted spiculitic rocks present in some mississippian reservoirs elsewhere in the mid continent cowley lithologies represent a low gradient ramp whereon 1 bedded spiculites were deposited in moderate energy shallow water inner ramp settings 2 lenticular nodular or flaser l n f bedded spiculite and shale were moderate to low energy progressively deeper water medial ramp deposits and 3 dark shales are deepest water outer ramp facies the internal stratigraphic architecture of the unconformity bounded cowley identifies it as a depositional sequence with component deepening upward basal strata transgressive systems tract overlain by shallowing upward progradational clinoforms highstand systems tract sequence deposition was punctuated by several unconformities attending short periods of subaerial exposure suppression of otherwise warm shallow water carbonate production and instead spiculite deposition in this low latitude setting was likely a consequence of elevated concentrations of dissolved silica and nutrients in the ambient marine environment three successive generations of silicification are recognized in the rocks early partial silicification is presumed to have begun in the marine environment and ensuing silicification and attendant porosity formation were likely coincident with falling sea level as pore fluids evolved from being of mixed marine meteoric to meteoric composition petroleum reservoirs mainly with vuggy porosity are present in relatively high porosity bedded spiculites and less porous l n f bedded rocks traps commonly are developed in structurally modified subunconformity buried hills and truncated gently dipping strata reservoirs in the l n f bedded rocks locally extend considerable distances downdip within individual clinoformal parasequences in the section thereby locally creating thick gas saturated reservoir columns because of its great subsurface extent the cowley section commonly bypassed during drilling offers considerable potential for as yet discovered fields in the mid continent

baselap patterns and the recognition of lowstand exposure and drowning a mississippian ramp example and its seismic signature abstract seismic sequence stratigraphy draws heavily upon analysis of stratal discordances to decipher the depositional history of a basin onlap and downlap which constitute two different classes of baselap are the most important types of discordances used to identify sequence boundaries in the absence of a regional grid of seismic lines from which the total stratal geometry can be documented however baselapping relationships are often misleading and misinterpreted class 1 baselap or onlap is frequently identified along seismic sequence boundaries but it may also he the most ambiguous lapout pattern to interpret onlap includes four subclasses subclass 1a platform proximal onlap onlap in the direction of the source of sediment supply subclass 1b basinal proximal onlap in the dir ction of the sediment source subclass 1c distal horizontal onlap onlap of horizontal bottomset in a direction away from the source of sediment supply and subclass 1d distal inclined onlap inclined bottomset onlapping an inclined surface class 2 baselap or downlap includes three subclasses horizontal downlap or subclass 2a describes initially inclined toeset strata that downlap an initially horizontal bottomset surface subclass 2b or climbing downlap in which toeset strata downlap a toeset and foreset surface inclined upward in the direction of lapout and subclass 2c or descending downlap describes toeset strata downlapping a foreset toeset surface inclined downward in the direction of sediment input the distinction between these types of baselap is important in aiding the reconstruction of relative sea level and depositional history as for example in resolving whether a carbonate platform bounded by baselapping strata was subjected to a sea level fall or a sea level rise a mississippian carbonate ramp exposed along the late paleozoic southern margin of north america demonstrates a dual history of lowstand exposure and transgressive drowning a sequence boundary sb345 developed at the end of osagean time by subaerial exposure at the top of a basinward prograding early mississippian carbonate ramp the resulting hiatus lasted as much as 10 m y and left a chert gravel residuum across the shelf in addition deltaic and shoreface systems prograded from the northeast and occupied a lowstand accommodation zone along the basinward margin of the ramp near the present mississippi embayment these lowstand deposits form a relatively thick downlapping wedge of siliciclastic strata above the early mississippian ramp and sb345 a late meramecian to chesterian s a level rise followed forcing the siliciclastic depositional systems to retrograde landward concomitantly carbonate sedimentation resumed across the flooded shelf and formed ooid and skeletal grain shoals carbonate sedimentation was short lived however because large quantities of mud derived from the ouachita orogen to the south encroached the shelf during the chesterian sea level rise forming an onlapping succession of black shale the rapid increase in accommodation space and the influx of suspended sediment and nutrients combined to submerge suffocate and poison the carbonate factory subaerial exposure and drowning led to formation of two baselap surfaces 1 a lowstand unconformity and 2 a drowning surface they lie so close to each other on the shelf however that s ismic discrimination is impossible at lower frequencies 35 50 hz synthetic seismic sections show reflections baselapping only one surface the lowstand unconformity when in fact there are two surfaces of very different origin at higher frequencies 75 100 hz baselap is visible at the drowning surface the paradox is that although the kinderhookian lower chesterian carbonate ramp was terminated by drowning the visible seismic baselap was due to lowstand exposure

lithofacies and sequence stratigraphy of the barnett shale in east central fort worth basin texas ten barnett shale lithofacies have been recognized in a 223 ft 68 m long core from johnson county texas eight of these lithofacies match those previously identified in the main producing area of the newark east barnett shale field in the northern part of the fort worth basin but two new lithofacies have been identified in this core resedimented spiculitic mudstone lithofacies and lag deposits both of which are indicative of a relatively higher energy environment and downslope resedimentation of shallower water deposits the recognition of cyclical stacking patterns of the lithofacies condensed sections css and transgressive surfaces of erosion were the keys to establishing the sequence stratigraphic framework in these fine grained rocks which consists of seven stratigraphic intervals in the lower barnett shale and nine stratigraphic intervals in the upper barnett shale spectral gamma ray uranium and thorium logs aided in this objective and are recommended for future sequence stratigraphic studies of these and other shales the sequence stratigraphic framework reveals that the lower barnett shale in this area was deposited mainly in a low energy relatively deep water environment somewhat far from a terrigenous source area which probably lies to the northwest by contrast the upper barnett shale was deposited in an oxygenated shallower water environment which had a source area from the west and southwest sides of the basin the higher frequency of sea level fluctuation during development of the upper barnett shale most probably indicates periodic tectonic activity perhaps associated with a structural high that was susceptible to sea level fluctuations alternatively it could have resulted from the onset of glaciations in gondwanaland during this time this higher frequency may indicate that the upper barnett is chesterian in age because cyclicity was higher than during the osagean and meramecian stages if so there may be more high frequency cycles than recognized in this core siliceous sponge spicules are more common in this core than in more northerly cores so more brittle facies might prevail in the southern part of the fort worth basin high gamma ray log responses which are caused by a high total organic carbon and or in situ phosphate minerals are commonly found in css and can be used for regional correlations however high gamma ray phosphatic deposits that have been resedimented to downslope positions by sediment gravity flows are an exception to the previous statement correlation of the barnett stratigraphic intervals now provides a north to southeast stratigraphic framework along the fort worth basin relative hydrocarbon potential rhp is an organic geochemical parameter applied to this core and found to provide an indicator of marine transgressions and regressions we recommend continued testing and use of the rhp parameter for high frequency sequence stratigraphic analysis of unconventional gas shales

subsurface structure of the eastern arkoma basin analysis of 425 km of seismic reflection data in the eastern arkoma basin reveals a structure and history quite different from those previously reported for the arkoma basin the eastern arkoma basin has three structural styles that formed in the following chronological order deep steep normal faults shallow listric normal faults and thrust faults the origin of the structural styles and the paleozoic history of the eastern arkoma basin may be summarized as follows late proterozoic or early cambrian rifting was followed by deposition of cambrian through upper mississippian strata on a passive plate margin the mississippian pennsylvanian boundary marks a time of major down to the south normal faulting with coincident folding of the footwall blocks and truncation of t e faulted and folded terrain by a pre morrowan mississippian pennsylvanian unconformity the unconformity slopes southward and steepens locally across the erosionally truncated footwall blocks during the pennsylvanian down to the south listric normal faults cut the atokan and morrowan sections and merged with but did not displace the steeper segments of the sub morrowan unconformity surface folds north of the ross creek thrust are rollover anticlines overlying these listric normal faults major deformation in the eastern arkoma basin terminated with emplacement of the ross creek thrust in the late pennsylvanian

hartshorne coal rank applied to arkoma basin coalbed methane activity oklahoma usa abstract coal rank generalized for all coal beds at or near the surface in the eastern oklahoma coalfield has been known since 1915 near the surface depths 305 m 1000 ft coals in arkoma basin coalbed methane cbm prospects was previously unknown a new hartshorne coal middle pennsylvanian rank map is based on mean maximum vitrinite reflectance values of 0 76 to 2 41 rmax from 70 coal samples from vertical depths of 0 surface to 1327 m 4355 ft hartshorne coal rank in the subsurface increases from high volatile bituminous to semianthracite from west to east in the arkoma basin in oklahoma bituminous rank boundaries changed considerably from earlier surface rank maps primarily by increasing the area of medium volatile bituminous rank coal in the subsurface and revealed a previously unknown semianthracite rank area this discrepancy is significant because the rank of deep 305 m 1000 ft coal resource assessments and cbm exploration projects have been based on shallow coal rank assignments a total of 2635 hartshorne hartshorne lower hartshorne and upper hartshorne cbm wells have been completed in oklahoma since 1988 most 1610 wells are horizontal with lateral lengths ranging from 4 to 1498 m 14 to 4914 ft an average of 669 m 2195 ft coal in most hartshorne cbm wells is medium volatile bituminous rank hartshorne coal is semianthracite rank in about 160 cbm wells in le flore county the four hartshorne cbm wells with the highest initial potential ip gas rates 48 to 65 thousand cubic meters per day mcmd 1 7 to 2 3 million cubic feet per day mmcfd are medium volatile bituminous rank from horizontal wells in haskell and pittsburg counties ip gas rates

aeolian processes across transverse dunes ii modelling the sediment transport and profile development this paper discusses a model which simulates dune development resulting from aeolian saltation transport the model was developed for application to coastal foredunes but is also applicable to sandy deserts with transverse dunes sediment transport is calculated using published deterministic and empirical relationships describing the influence of meteorological conditions topography sediment characteristics and vegetation a so called adaptation length is incorporated to calculate the development of transport equilibrium along the profile changes in topography are derived from the predicted transport using the continuity equation vegetation height is incorporated in the model as a dynamic variable vegetation can be buried during transport events which results in important changes in the sediment transport rates the sediment transport model is dynamically linked to a second order closure air flow model which predicts friction velocities over the profile influenced by topography and surface roughness modelling results are shown for a the growth and migration of bare initially sine shaped dunes and b dune building on a partly vegetated and initially flat surface results show that the bare symmetrical dunes change into asymmetric shapes with a slipface on the lee side this result could only be achieved in combination with the secondorder closure model for the calculation of air flow the simulations with the partly vegetated surfaces reveal that the resulting dune morphology strongly depends on the value of the adaptation length parameter and on the vegetation height the latter result implies that the dynamical interaction between aeolian activity and vegetation reaction to burial growth rates is highly relevant in dune geomorphology and deserves much attention in future studies copyright 1999 john wiley sons ltd

the stabilizing role of bonding agents on the entrainment of sediment by wind well sorted fine sand pretreated with varying concentrations of two soluble salts mgcl2 and cacl2 was tested for threshold shear velocity in a recirculating wind tunnel these tests demonstrate that even relatively low surface salt concentrations can significantly increase threshold shear velocity however the relationships between surface salt concentration and threshold shear velocity for the two salts were not significantly different which is similar to the results for monovalent chlorides presented by nickling ecclestone a general relationship between threshold shear velocity and total surface soluble salt content is presented

on the origin and age of the great sand dunes colorado abstract over the past 100 yr several hypotheses have been proposed for the origin and age of the great sand dunes these hypotheses differ widely in the descriptions of dune morphometry the immediate source of eolian sand and when sand transport occurred the primary purpose of this paper is to evaluate these hypotheses and where warranted to present new ideas about the origin and age of the great sand dunes to evaluate the previous hypotheses we had to develop more detailed information about the surficial geology of the northern san luis valley thus we mapped the surficial geology of an area extending several tens of kilometers north south and west of the great sand dunes and examined subsurface stratigraphy in more than 200 wells and borings in addition we used relative dating criteria and several radiocarbon and osl ages to establish the chronology of surficial deposits and we determined the u pb ages of detrital zircons to obtain information about the sources of the sand in the great sand dunes the first principal finding of this study is that the lower part of the closed basin north of the rio grande referred to here as the sump is the immediate source of the sand in the great sand dunes rather than the late pleistocene flood plain of the rio grande the most widely accepted hypothesis a second principal finding is that the great sand dunes are older than late pleistocene they postdate the draining of lake alamosa which began 440 ka and predate the time when streams draining the west flank of the sangre de cristo mountains were deflected by incipient dunes that formed near the mountain front geomorphic and stratigraphic evidence indicate that this deflection occurred prior to the end of the next to last glaciation bull lake i e prior to 130 ka

diurnal winds in the himalayan kali gandaki valley part i observations abstract the diurnal wind system of the kali gandaki valley in nepal was explored in september and october 1998 in a field campaign using pilot balloons as the main observational tool this valley connects the plateau of tibet with the indian plains the river crosses the himalayas forming the deepest valley on earth intense upvalley winds blow up this valley during the day observations were made along the river at various spots selected between the exit point from the himalayas and the source close to the plateau of tibet the strongest upvalley winds were found between marpha and chuksang with typical speeds of 15 20 m s 1 the upvalley wind sets in first at the ground but an upvalley wind layer of 1000 2000 m depth forms quickly after the onset this deep inflow layer persists up to lo manthang a town located a few kilometers south of the plateau of tibet deceleration in the late afternoon and evening also appears to commence near the ground weak drainage flow forms late in the night the causes o

wind tunnel investigation of the influence of surface moisture content on the entrainment and erosion of beach sand by wind using sands from tropical humid coastal southern china abstract wind erosion has major impacts on dune growth desertification and architecture on sea coasts the deflation threshold shear velocity is a crucial parameter in predicting erosion and surface moisture greatly affects this threshold and thus sand stability wind tunnel studies have shown that reduced moisture contents decrease entrainment thresholds and increase wind erosion but field and wind tunnel test data is lacking for tropical humid coastal areas in this study we investigated the influence of surface moisture contents at 1 mm depth on sand entrainment and erosion using tropical humid coastal sands from southern china shear velocities were deduced from velocity profiles above the sand the threshold shear velocity increased linearly with increasing ln100 m m gravimetric moisture content the increase was steepest below a moisture content of 0 0124 i e at m 1 5 the moisture content in the sand at a matric potential of 1 5 mpa we compared several popular models that predict threshold shear velocity of moisture sediment and found substantial differences between their predicted results at a surface moisture content of 0 0124 the predicted increase in the wet threshold shear velocity compared with the dry threshold shear velocity ranged from 34 to 195 the empirical model of chepil and selah simulated the data well for m m 1 5 whereas belly s empirical model simulated the data best for m 0 0062 wind erosion modulus increased with increasing effective wind velocity following a power function with a positive exponent at all moisture contents but decreased with increasing surface moisture content following a power function with a negative exponent when wind speed and moisture content varied simultaneously wind erosion modulus was proportional to the 0 73 power of effective wind velocity but inversely proportional to the 1 48 power of m the increase in resistance to erosion at low moisture contents probably results from cohesive forces in the water films surrounding the sand particles at a moisture content near m 1 5 wind erosion ceases nearly for all wind velocities that we tested

recognizing and quantifying expulsion of oil from the woodford formation and age equivalent rocks in oklahoma and arkansas accumulations of oil in fractures stylolites burrows sandstone lenses and chert nodules deeply embedded within organic rich mature oil source beds of late devonian early mississippian age are considered prima facie evidence of internal migration and expulsion most oil migrated internally and was expelled as a separate phase within a given section in which chert and black shale are interbedded contain the same type of organic matter and have reached the same level of thermal maturity black shales typically contain less hydrocarbons per weight percent toc than cherts the observed differences represent the amount of oil expelled from the black shales and range from 10 to 15 mg g toc for total bitumen 7 to 8 mg g toc for saturated hydrocarbons and 11 mg g toc for volatile hydrocarbons approximately 27 33 of the oil generated in these source rocks was calculated to have been expelled in the main oil producing region of central and southern oklahoma 22 billion bbl of bitumen and 16 billion bbl of saturated hydrocarbons were estimated to have been expelled from the woodford formation relatively efficient separate phase oil expulsion may be characteristic of very rich oil source rocks like those reported here such rocks would reach effective oil saturation and begin to expel oil as a separate phase at a relatively early stage of generation timing and efficiency of oil expulsion must then be influenced by the concentration and type of organic matter in the source rock because these factors determine the volume of oil generated and hence the time when a source rock becomes oil saturated

threshold friction velocities and rupture moduli for crusted desert soils for the input of soil particles into the air desert soils having clay crusts mostly from the mojave desert were tested for threshold friction velocity the friction velocity at which soil erosion begins with an open bottomed wind tunnel the soils were also tested for content of clay water soluble material calcium carbonate organic material mineralogy of clay and of salts soil moisture modulus of rupture and crust thickness if no loose material existed on the soil surface crusts having modulus of rupture greater than 0 7 bar and crust thickness of 0 7 cm to 0 3 cm were effective in protecting against wind erosion disturbed clay crusts having modulus of rupture before disturbance greater than 2 bar with thickness less than 1 9 cm did not experience significant wind erosion modulus of rupture was related to composition of soil but was shown to depend mostly on clay content soil composition is related to modulus of rupture in an empirical equation

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

climate induced sediment palaeosol cycles in a late cretaceous dry aeolian sand sheet marilia formation north west bauru basin brazil aeolian sand sheets which are characterized by low relief surfaces that lack dunes are common in arid and semi arid climatic settings the surface of an aeolian sand sheet can either be stable and subject to pedogenetic effects or unstable such that it is affected by deflation or sedimentation the maro lia formation late cretaceous may be interpreted as an ancient aeolian sand sheet area where alternating phases of stability and instability of the accumulation surface have been recorded detailed field studies were carried out in several sections of the maro lia formation where cyclic alternations of palaeosols and aeolian deposits were evident using palaeopedological and facies analysis methods supported in the laboratory by the analysis of rock samples cut and polished in slabs thin sections scanning electron microscope images and x ray diffraction data from the clay minerals the deposits comprise three lithofacies that in order of abundance are characterized by i translatent wind ripple strata ii flood deposits and iii ephemeral river channel deposits palaeosols constitute on average 65 of the vertical succession three types of palaeosols pedotypes are recognized i aridisols ii entisols and iii vertisols erosional surfaces due to aeolian deflation divide the top of the palaeosol profiles from the overlying aeolian deposits the palaeoenvironmental interpretation of the deposits and the palaeosols allows the depositional system of the maro lia formation to be defined as a flat area dominated by aeolian sedimentation with subordinate ephemeral river sedimentation and characterized by a dry climatic setting with occasional rainfall the climate is the main forcing factor controlling the alternation between episodes of active sedimentation and periods of palaeosol development a climate controlled model is proposed in which i the palaeosols are indicative of a stable surface that is developed during the more humid climatic phases and ii the erosional surfaces and the overlying aeolian sediments attest to periods of deflation and subsequent sedimentation thereby increasing the availability of sediment during the drier climatic phases the ephemeral fluvial deposits mark the more humid climatic conditions and contribute to the lagged sediment influx caused during the drier periods by the erosion of previously stored sediment

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

mechanisms of up valley winds abstract the basic physical mechanisms governing the daytime evolution of up valley winds in mountain valleys are investigated using a series of numerical simulations of thermally driven flow over idealized three dimensional topography the three dimensional topography used in this study is composed of two two dimensional topographies one a slope connecting a plain with a plateau and the other a valley with a horizontal floor the present two dimensional simulations of the valley flow agree with results of previous investigations in that the heated sidewalls produce upslope flows that require a compensating subsidence in the valley core bringing down potentially warmer air from the stable free atmosphere in the context of the three dimensional valley plain simulations the authors find that this subsidence heating in the valley core is the main contributor to the valley plain temperature contrast which under the hydrostatic approximation is the main contributor to the valley plain pressure differe

diurnal winds in the himalayan kali gandaki valley part ii modeling abstract the penn state ncar mesoscale model mm5 is used to simulate and better understand the wind observations in the kali gandaki valley reported in the first part of this paper the kali gandaki river originates in nepal near tibet flows southward through the mustang basin crosses the himalayas in a gorge and descends to the lowlands of nepal extremely strong diurnal upvalley flow in the gorge and the basin alternates with rather weak drainage flow in the night as proposed in part i the mustang basin and the tibetan plateau can be considered as an elevated heat source driving the upvalley flow during the day however the extreme strength of the diurnal upvalley winds and the order of magnitude asymmetry between day and night cannot be explained with a simple plateau circulation theory the model is successful in simulating almost all aspects of the observations the simulations strongly suggest that the observed acceleration of the upvalley winds near the entrance to the mustang basin is linked

wind initiation thresholds of the moistened sands 1 the widely accepted bagnold type function for calculating threshold wind velocity or shear velocity was developed for dry sands but surface moisture is an extremely important variable controlling the entrainment process of sands by wind because the tensile force between the water molecules and sand grains produces cohesion here we report detailed wind tunnel experimental results on the threshold shear velocity of moistened sand of different sizes the results show that relative threshold shear velocity which is the ratio of threshold shear velocity of sand in the moistened state to that in the dry state is better related to moisture content than threshold shear velocity itself function modified after the bagnold equation has been developed to estimate the threshold shear velocities of moistened sands for a given grain size the threshold shear velocity is proportional to 1 km 1 2 where m is the moisture content and k is a coefficient depending on grain size

climate surface pore water interactions on a salt crusted playa implications for crust pattern and surface roughness development measured using terrestrial laser scanning sodium accumulating playas also termed sodic or natric playas are typically covered by polygonal crusts with different pattern characteristics but little is known about the short term hours dynamics of these patterns or how pore water may respond to or drive changing salt crust patterning and surface roughness it is important to understand these interactions because playa crust surface pore water and roughness both influence wind erosion and dust emission through controlling erodibility and erosivity here we present the first high resolution 10 3m hours co located measurements of changing moisture and salt crust topography using terrestrial laser scanning tls and infra red imagery for sua pan botswana maximum nocturnal moisture pattern change was found on the crests of ridged surfaces during periods of low temperature and high relative humidity these peaks experienced non elastic expansion overnight of up to 30 mm and up to an average of 1 5 mm night during the 39 day measurement period continuous crusts on the other hand showed little nocturnal change in moisture or elevation the dynamic nature of salt crusts and the complex feedback patterns identified emphasise how processes both above and below the surface may govern the response of playa surfaces to microclimate diurnal cycles

a two dimensional simulation of the iberian summer thermal low abstract the forcing mechanisms of the diurnal thermal depression formed over the iberian peninsula in the summer and the typical air circulation induced over the northern plateau are analyzed by a two dimensional hydrostatic high resolution primitive equation model applied in a vertical plane perpendicular to the coastline of the bay of biscay such circulation is characterized by a low level flow of relatively cold air that progresses inward over the elevated central plateau throughout the afternoon and evening reaching inland distances up to 150 km at dawn which tends to fill up the already formed thermal depression despite the simplicity of the model the results obtained show a satisfactory agreement with observations finally a comparison is made between results obtained from a set of simulations with different combinations of land use types topographic profiles thermal stability and synoptic wind keeping the other conditions fixed in order to analyze the individual effects of different t

on the effect of moisture bonding forces in air dry soils on threshold friction velocity of wind erosion wind erosion is a dominant geomorphological process in arid and semi arid regions with major impacts on regional climate and desertification the erosion process occurs when the wind speed exceeds a certain threshold value which depends on a number of factors including surface soil moisture the understanding and modelling of aeolian erosion requires a better understanding of the soil erodibility associated with different moisture conditions in arid regions during the dry season the atmospheric humidity plays an important role in determining the surface moisture content and the threshold shear velocity by a series of wind tunnel tests and theoretical analyses this dependence of threshold velocity on near surface air humidity is shown for three soils of different textures sand sandy loam and clay loam the results show that the threshold shear velocity decreases with increasing values of relative humidity for values of relative humidity between about 40 and 65 while above and below this range the threshold shear velocity increases with air humidity a theoretical framework is developed to explain these dependencies assuming an equilibrium between the surface soil moisture and the humidity of the overlying atmosphere the conditions under which soil atmosphere equilibrium occurs were tested experimentally in the laboratory for different soils in order to determine the effect of grain surface area and texture on the time required to reach equilibrium starting from different initial conditions

diagenesis of an overmature gas reservoir the spiro sand of the arkoma basin usa abstract the spiro sand is a laterally extensive thin sandstone of earliest atokan pennsylvanian age that forms a major natural gas reservoir in the western arkoma basin oklahoma petrographic analysis revelas a variety of diagenetic alterations the majority of which occurred during moderate to deep burial early diagenetic processes include calcite cementation and the formation of fe clay mineral peloids and coatings around quartz framework grains these clays which underwent transformation to well crystallized chamosite polytype lb 90 c these clays are particularly abundant in medium grained channel sandstones whereas illitic clays are predominant in fine grained interchannel sandstones subsequent to mechanical compaction saddle ankerite precipitated in the reservoir at temperatures in excess of 70 c crude oil collected in favourable structural locations during and after ankeritization whereas hydrocarbons apparently halted inorganic diagenesis in oil saturated zones cementation continued in the underlying water saturated zones as reservoir temperatures increased further hydrocarbons were cracked and a solid pyrobitumen residue remained in the reservoir at temperatures exceeding 140 150 c non syntaxial quartz cement ferroan calcite and traces of dickite locally reduced the reservoir quality local secondary porosity was created by carbonate cement dissolution this alteration post dated hydrocarbon emplacement and is probably related to late stage infiltration of freshwater along leaky faults the study shows that the spiro sandstone locally retained excellent porosites despite deep burial and thermal conditions that correspond to the zone of incipient very low grade metamorphism

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

rates of aeolian transport on a beach in a temperate humid climate short term field measurements of aeolian transport using a saltiphone indicate that actual rates of transport deviate considerably from the potential rates predicted by transport equations when examined in detail however potential rates are approached during special conditions mostly when the wind blows offshore parallel or slightly oblique to the beach and relative humidity is below 85 also the potential rates of transport may be approached when wind speeds considerably exceed threshold speed even during showers the main cause of the large deviation of actual from potential rates is in the absence of transport during very wet conditions prolonged rainfall regardless of wind speed and the variation of threshold velocity with time the threshold velocity increases during wet conditions with onshore winds or because of the presence of algae therefore potential transport is defined as the transport optimum to predict the actual rates of transport accurately insight into the variation of the threshold velocity is essential aeolian transport of sand seems to be related to moderate events and not to extreme events conforming to the principle of magnitude and frequency

geologic model building in seam phase ii land seismic challenges three digital earth models were designed and constructed during seam phase ii to study exploration challenges at the scale of modern land seismic surveys although built as generic models each was based on one or more related geologic type areas the barrett model represents the seismic anisotropy of complex laminated and fractured shale reservoirs based on the woodford and eagle ford formations and set below a stratigraphic overburden and near surface of a north american midcontinent basin the arid model features the extreme property contrasts of desert terrains in a 500 m thick near surface that juxtaposes hard carbonate bedrock and soft sediments filling karsts typical of the saudi arabian peninsula the foothills model contains sharp surface topography and alluvial fan like sediments above complex fold and thrust structures based on the compressive tectonics of the llanos foothills of south america all three models were built in workflows that combined automated steps with a large measure of manu

orographic rainfall hot spots in the andes amazon transition according to the trmm precipitation radar and in situ data the andes amazon transition along the eastern peruvian andes features hotspots with strong precipitation using 15 years of trmm pr data we established a robust relation between terrain elevation and mean surface precipitation with the latter peaking around 1000 masl coinciding with the moisture flux peak of the south american low level jet sallj there is strong diurnal variability with afternoon 13 18 lt convection in the amazon plains while on the eastern slopes 1000 2000 masl after the forcing associated with the thermal heating of the andes subsides convection grows during the night and surface precipitation peaks around 01 06 lt and organizes into mesoscale convective systems mcss these then displace downslope to an terrain elevation of 700 masl with stratiform regions spreading upslope and downslope and then decay during the remainder of the morning the large mcss contribute with at least 50 of daily rainfall 40 of the 01 06 lt rainfall on synoptic scales the large mcss are more common in stronger sallj conditions although subtropical cold surges are responsible for 16 of the cases

an improved method for computing horizontal diffusion in a sigma coordinate model and its application to simulations over mountainous topography abstract a set of modifications is presented to reduce the unphysical impact of horizontal diffusion in numerical models with a terrain following sigma coordinate system at model levels sufficiently far away from the ground vertical interpolation is used to compute diffusion truly horizontally when the coordinate surfaces are sloping close to the ground where truly horizontal computation of diffusion is not everywhere possible without intersecting the topography a combination of one sided truly horizontal diffusion and orography adjusted diffusion along the sigma surfaces is used for most of the variables the latter means that the diffusion coefficient is reduced strongly when the grid points involved in the computation of horizontal diffusion are located at greatly different heights for temperature one sided horizontal diffusion is not used because it damps the slope wind circulation in an unphysical way however a temperature gradient correction is applied to the terrain following part of the t

the mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern negev israel

aeolian sediment supply at a mega nourishment abstract mega nourishments are intended to enhance growth and resilience of coastal dunes on medium to long time scales by stimulation of natural sediment transport processes the growth and resilience of coastal dunes largely depends on the presence of a continuous supply of aeolian sediment a recent example of a mega nourishment is the 21 mm 3 mega nourishment known as the sand motor the sand motor is intended to nourish the entire holland coast over a period of two decades four years of bi monthly topographic measurements of the sand motor domain provide an opportunity to analyze spatiotemporal variations in aeolian sediment supply using an aeolian sediment budget analysis it appears that more than 58 of all aeolian sediment deposits originate from the low lying beaches that are regularly reworked by waves aeolian sediment supply from higher beaches diminished after half a year after construction of the sand motor likely due to the formation of deflation lag deposits that constitute a beach armor layer the compartmentalization of the sand motor in armored and unarmored surfaces suggests that the construction height is an important design criterion that influences the lifetime and region of influence for any mega nourishment

nearest neighbor analysis of mega barchanoid dunes ar rub al khali sand sea the application of geographical indices to the understanding of dune field self organization maturity and environmental change abstract the geographic signature of dune distribution and self organization as measured by the r statistic offers a viewpoint on the geography of crescentic aeolian systems and proposes an index from which to determine the degree of self organization maturity and possibly relative age across a variety of spatial scales and planetary contexts this analogue study examines and compares the geography of crescentic megadune patterns for the al liwa basin of the ar rub al khali sand sea on the arabian peninsula fields of mega barchanoid forms have shown the degree of self organization to be largely an association between morphological diversity and dimensional variability in short fields of transitional megadunes barchanoid seif are comparatively less regular in distribution than are those fields or part thereof that consist of ubiquitous compound barchanoid morphologies whose patterns are more highly regular the change in dune morphology dimensions and spatial signature can for the most part be associated with the directional differences and varying intensities of the north westerly shamal and reversing south westerly kharif wind regimes such associations have significant bearing on the maturity of dunefields and their response to sediment supply transport capacity and sediment availability within an aeolian system this study provides an analogue on which to base further comparative studies with other terrestrial dune fields as well as the ergs and intracrater fields of mars

mechanisms of dust emission from pleistocene loess deposits nebraska usa 1 saltation bombardment is commonly believed to be the primary mechanism by which large quantities of dust can be generated direct entrainment of silt on the other hand is thought to generate minimal quantities of dust if so loess landscapes should rarely be major sources of dust unless disturbed by human activity to test the mechanisms by which loess can be eroded by the wind we used the portable in situ wind erosion lab pi swerl pi swerl tests were conducted on benches that were carved into loess at field locations coarse to fine loess was also collected and tested in a controlled setting using 1 dry unconsolidated loess and 2 crusted loess results indicate that in most cases the threshold friction velocity for silt is less than that for sand and that most dust generation occurs by direct entrainment of dust saltation even in coarse loess was nonexistent to intermittent in a few cases saltation of sand or soil aggregates preceded dust generation or enhanced emissions after direct entrainment began emission fluxes of loess are potentially high in both proximal and distal settings suggesting that loess is easily entrainable if vegetation density is low we hypothesize that an arid and windy climate of the late pleistocene paired with lower vegetation density facilitated large scale erosion of peoria loess in nebraska to generate wind aligned ridges and troughs more broadly our results indicate that loess landscapes have the potential to be major sources as well as sinks of dust

regional scale flows in mountainous terrain part ii simplified numerical experiments abstract a series of two and three dimensional idealized numerical experiments are conducted to examine the effects of different physical processes upon the development of the thermally driven regional scale circulations over mountainous terrain simulated in part i the goal of this paper is to understand the conditions that enhance or suppress the formation of a westward propagating density current within the mountain boundary layer this current evolves from the front range mountain plain circulation and was found in part i to be responsible for unusual wind phenomena observed at mountaintop locations during the rocky mountain peaks experiment over western colorado the idealized experiments show that the westward propagating density current is a robust feature under summertime conditions of weak ambient flow and is initiated by differential heating across the colorado front range between the plains and the intermountain region in addition the longevity of the thermally driven circulation system indu

aeolian transport of sediment on a beach during and after rainfall wildwood nj usa abstract a field investigation was conducted 9 march 1994 on a dissipative beach to compare wind characteristics and aeolian transport during and after a light rain winds blew alongshore during the monitoring period moisture content of surface sediment on the backbeach was above 7 during rain and 4 four hours after rainfall ceased trapping rates measured using a cylindrical vertical trap were 14 1 kg m 1 h 1 during rainfall and 140 2 kg m 1 h 1 for a period beginning 3 h 33 min after rainfall ceased results indicate that light rain resulting in bulk surface moisture values over 7 is not sufficient to eliminate transport but the rate of transport is lower than can occur on the beach three to four hours following rain the amount of sand trapped at wildwood during rainfall is relatively high when compared to many previous studies on beaches in the absence of rain the great length of the beach as a source area combined with parallel or oblique winds are significant in increasing rates of sediment transport

organic geochemistry of the woodford shale southeastern oklahoma how variable can shales be woodford shale samples obtained from a cored outcrop in southeastern oklahoma were geochemically analyzed to determine vertical variations of organic facies thermal maturity and an evaluation of their depositional environments total organic carbon values ranged from 5 01 to 14 81 indicating a good source rock potential in this area the woodford shale is marginally mature as indicated by vitrinite reflectance values rock eval data revealed that the samples are dominated by type ii kerogen biomarker ratios based on pristane phytane steranes and hopanes show a mix of marine and terrigenous organic matter high salinity conditions and water density stratification also prevailed during deposition of this formation as indicated by the presence of gammacerane the woodford shale was subdivided into lower middle and upper members based on the integration of geochemical and geologic data moreover the presence and extent of photic zone anoxia pza were determined by the presence of aryl isoprenoids the lower and upper woodford shale members were deposited under dysoxic to suboxic conditions and episodic periods of pza the middle member was deposited under anoxic conditions and persistent pza in addition aryl isoprenoids helped infer the position of the chemocline during deposition of the different members the relative hydrocarbon potential parameter was used in determining transgressive and regressive cycles within the woodford shale this study undoubtedly demonstrates the significant lithologic and chemical variability that occurs within shales the application of this workflow to regional studies can have a direct influence on exploration and production activities in shale gas systems

the thermal circulation of a grand plateau sensitivity to the height width and shape of the plateau abstract idealized numerical simulations are presented to investigate the sensitivity of the thermal plateau circulation to the plateau height width and the presence of a mountain ridge encompassing the plateau the study concentrates on plateaus surrounded by land with the same surface properties so that the topography is the only source of differential heating for low plateaus it is found that the strength of the plateau circulation increases with the plateau height because the excess heating of the plateau increases with its height the plateau circulation reaches its maximum strength for plateau heights similar to the mixed layer depth over the surrounding lowlands for even higher plateaus the depth of the circulation decreases whereas the peak intensity exhibits little change the plateau height also controls the temporal evolution of the plateau circulation for low plateaus low level inflow is primarily found during the night because convection cells forming over the lateral slopes prevent a

aeolian slipface dynamics and grainflow morphologies on earth and mars abstract in 2015 an active dune field on mars was visited up close by the curiosity rover in gale crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital based imagery for the first time these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations the image data from the slipface on the namib dune within the bagnold dune field shows grainflow morphologies that are similar to dunes on earth quantitative estimates of flow thickness based on shadow length are presented for the grainflows on the namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the maspalomas dune field located in gran canaria spain using observations from maspalomas to support interpretations of martian slipface dynamics we discuss implications for the local wind regime style of grainflow seasonal activity and dune migration the presence of multiple large magnitude grainflows on the namib slipface suggests an active aeolian environment capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope however the thinness of grainflows on the namib dune the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment at least for the most recent slipface activity large actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events this mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies both young and old which are otherwise quickly erased on earth due to sediment redistribution and grainfall

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

the role of wind direction in eolian transport on a narrow sandy beach comparison of eolian transport during five high velocity wind events over a 29 day period on a narrow estuarine beach in delaware bay new jersey usa reveals the temporal variability of transport due to changes in direction of wind approach mean wind speed measured 6 m above the dune crest for the five events ranged from 8 5 to 15 9 ms 1 mean wind direction was oblique to the shoreline 63 from shore normal during one event but was within 14 of shore normal during the other events eolian transport is greatest during low tide and rising tide when the beach source area is widest and when drying of surface sediments occurs the quantity of sediment caught in a vertical trap for the five events varied from a total of 0 07 to 113 73 kgm 1 differences in temperature relative humidity and moisture and salt content of surficial sediments were slight mean grain sizes ranged from 0 33 to 0 58 mm causing slight differences in threshold shear velocity but shear velocities exceeded the threshold required for transport during all events beach width measured normal to the shoreline varied from 15 5 to 18 0 m beach slope differed by 0 5 the oblique wind during one event created a source width nearly double the width during other days beach slope measured in the direction of the wind was less than half as steep as the slope measured normal to the shoreline the amount of sand trapped during the oblique wind was over 20 times greater than any other event even those with higher shear velocities the ability of the beach surface to supply grains to the air stream is limited on narrow beaches but increased source width due to oblique wind approach can partially overcome limitations of surface conditions on the beach

thermal maturity of carboniferous strata ouachita mountains the ouachita mountains a relatively untested potential hydrocarbon province contain a thick paleozoic section of apparently favorable source beds reservoir beds and trap configurations to estimate the thermal maturity of these strata vitrinite reflectance was measured on 89 samples collected mostly from carboniferous rocks from throughout the ouachita outcrop area thermal maturity contours generally parallel structural grain in the western two thirds of the ouachitas reflectance values in oil range from 3 0 in the core area in oklahoma and from about 1 0 to 3 0 in analogous positions in arkansas older strata on upthrown sides of thrust faults are more thermally mature than younger strata on downthrown sides in the eastern one third of the outcrop belt thermal maturities are significantly higher 2 0 5 0 ro and thermal maturity contours cut obliquely across structural grain strata on either side of thrust faults display identical levels of maturity in the western two thirds of the ouachitas sedimentary and tectonic burial have been the major influences of thermal maturation although a mesozoic thermal overprint has increased levels of maturity in arkansas throughout this area strata are within the oil and wet gas windows the anomalous levels and patterns of thermal maturity in the eastern third of the ouachitas are probably the result of a thermal overprint related to mesozoic rifting and intrusive activity in the mississippi embayment this thermal overprint has elevated the maturity of strata in most of this area above the level of hydrocarbon preservation although maturities within the dry gas window are retained locally

quantifying dust emissions from desert landforms eastern mojave desert usa abstract the measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models more than 500 individual dust measurements from eight common desert landforms in southern california were collected using the pi swerl portable in situ wind erosion lab the largest emitters of dust are dry washes 13 787 to 0 007 mg m 2 s 1 dunes playa margins distal alluvial fans and lacustrine beaches low emitters include salt crusted playas 0 692 to 0 002 mg m 2 s 1 silt clay crusted playas and desert pavements high emissions are a function of saltating sand that bombards the surface liberating dust sized particles for entrainment low dust emissions are primarily a function of surface crusting gravel armoring and vegetation density pi swerl measurements reveal that emission rates can vary by at least three orders of magnitude reflecting local variability in soil texture and continuity of surface crusts shear stress partitioning models can be applied to dust data measured by the pi swerl to account for large surface roughness features such as vegetation the results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the mojave desert and can potentially be used to improve atmospheric dust models

the effect of surface moisture on the entrainment of dune sand by wind an evaluation of selected models reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not among the several factors that govern the initiation of soil movement by wind surface moisture is one of the most significant some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated wind tunnel experiments were conducted on pre wetted dune sand with moisture contents ranging from 0 00 to 0 04 kg kg 1 sand samples were exposed to different wind speeds for 2 min moisture content was determined gravimetrically before and after each experiment and the saltation of sand particles was recorded electronically with a saltiphone shear velocities were deduced from the wind speed profiles for each moisture content the experiments were repeated at different shear velocities with the threshold shear velocity being determined by least squares analysis of the relationships between particle number rates and shear velocity within the 2 min test runs temporal changes in particle number rates and moisture contents were detected a steep increase in the threshold shear velocity with moisture content was observed when comparing the models large differences between the predicted results became apparent at a moisture content of 0 007 kg kg 1 which is half the moisture content retained to the soil matrix at a water tension or matric potential of 1 5 mpa the increase in wet threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117 to 171 the highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment nevertheless the models of chepil 1956 proc soil sci soc am 20 288 292 and saleh fryrear 1995 soil sci 160 304 309 are the best alternatives available

summer thermal lows in the iberian peninsula a three dimensional simulation a summary of some of the most relevant climatological characteristics of summer thermal lows in the iberian peninsula is given followed by a description of a high resolution numerical model which has been used to simulate the mesoscale system of a typical summer s day the results from this model show the appearance of small low pressure centres before noon one of which prevails over the others and intensifies during the afternoon other small size structures related to this system and not evident in the analysis from the ecmwf european centre for medium range weather forecasts forecast model appear in the simulation such as the existence of areas with strong convergence near the surface and the deviation towards the interior of the peninsula of the surface winds as the depression intensifies also the structures associated with certain variables such as potential temperature vertical velocity and potential vorticity become more noticeable in the model s simulation compared with the ecmwf analysis finally a detailed description of the dynamical development of the simulated surface low pressure system is presented taking all these findings into consideration

multiscale analysis of the summertime precipitation over the central andes precipitation over the central andes in south america exhibits a marked annual march with most of the rainfall concentrated during the austral summer season december february when the atmospheric circulation favors the uplifting of moist air from the lowlands to the east of the mountain range within its rainy season the central andes experiences week long rainy and dry episodes the large scale and local conditions during these episodes are investigated using satellite imagery reanalyzed atmospheric fields and in situ data despite the deep layer of conditional instability prevalent during most summertime afternoons deep convection can occur only on those days in which the mixing ratio within the local boundary layer exceeds some threshold 7gk g 21 yielding saturation of near surface air parcels rising more than 600 m above ground convective cloudiness anomalies over the central andes extend southeastward and tend to be concurrent with anomalies of opposite sign over the eastern part of the continent rainy dry episodes are also associated with anticyclonic cyclonic anomalies centered over subtropical south america that extend through the depth of the troposphere accompanied by easterly westerly wind anomalies over the central andes these anomalies are presumably forced by planetary waves originating in the southern hemisphere extratropics to gain insight into the regional processes linking the large scale and local conditions the pennsylvania state university national center for atmospheric research mesoscale model version 5 2 was used to simulate contrasting rainy and dry episodes the most marked and relevant differences are the strength and extent of diurnally varying flow over the eastern slope of the andes during the rainy simulation strong easterly winds reach the upper part of the slope by midmorning initiating an intrusion of warm and moist air high ue air originating in the eastern lowlands into the central andes in the dry case the moisture transport from the east is restricted to the eastern slope of the andes and the central andes is flooded by low ue air from the western foothills that cannot support deep convection even in the presence of localized updrafts the momentum balance based on the model output indicates that turbulent momentum mixing from aloft determined by the large scale anomalies of the upper level flow into the convective boundary layer is the leading term causing the differences in the daytime upslope flow and hence moisture transport over the upper part of the eastern side of the andes between rainy and dry simulations

sedimentology and development of parabolic dunes grande prairie dune field alberta the grande prairie dune field in northwest central alberta is composed of parabolic and dome dunes presently inactive but which had developed under westerly winds two parabolic dune types are rec