provenance and transport process for interdune sands in the kumtagh sand sea northwest china abstract interdune areas are an important part of dune systems as they affect dune evolution and sand sea development however there has been little work on the provenance of interdune sediments our lack of knowledge of these sediments prevents a more complete understanding of sand sea formation and evolution in the present study we focused on the provenance of interdune sediments in the kumtagh sand sea based on their granular mineral and geochemical characteristics then further identified the spatial scope of the contribution of these sources to the interdune sediments and the associated transport mechanisms although sediment supply analysis suggested that the interdune sand may derive from the altyn tagh mountains beishan mountains and sanlongsha dune field the provenance signature based on the k rb and k ba ratios revealed that the ultimate sources were the altyn tagh mountains in the south and the beishan mountains in the north by plotting the identified provenance results on a map of the sand sea we found that the spatial scopes of contributions from these sources were separated at around 40 n however the existence of a fluvial load em1 and of reworked coarse particles em3 in the northern sand sea demonstrated that the interdune sands in this region were partly derived from the altyn tagh mountains in the south consequently by combining our results with the transport agents condition we concluded that the altyn tagh mountains supplied sediments to interdune areas by fluvial transport throughout the sand sea but that sediment in the northern sand sea was subsequently reworked and mixed with windblown sand originated from the beishan mountains

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

mcget a rapid image based method to determine the morphological characteristics of gravels on the gobi desert surface abstract the relationship between morphological characteristics e g gravel size coverage angularity and orientation and local geomorphic features e g slope gradient and aspect of desert has been used to explore the evolution process of gobi desert conventional quantification methods are time consuming inefficient and even prove impossible to determine the characteristics of large numbers of gravels we propose a rapid image based method to obtain the morphological characteristics of gravels on the gobi desert surface which is called the morphological characteristics gained effectively technique mcget the image of the gobi desert surface was classified into gravel clusters and background by a machine learning classification and regression tree cart algorithm then gravel clusters were segmented into individual gravel clasts by separating objects in images using a watershed segmentation algorithm thirdly gravel coverage diameter aspect ratio and orientation were calculated based on the basic principles of 2d computer graphics we validated this method with two independent datasets in which the gravel morphological characteristics were obtained from 2728 gravels measured in the field and 7422 gravels measured by manual digitization finally we applied mcget to derive the spatial variation of gravel morphology on the gobi desert along an alluvial proluvial fan located in hami xinjiang china the validated results show that the mean gravel diameter measured in the field agreed well with that calculated by mcget for large gravels r2 0 89 p

a hydrocarbon exploration model for the cretaceous ferron sandstone member of the mancos shale and the dakota group in the wasatch plateau and castle valley of east central utah with emphasis on post 1980 subsurface data ofr 160

the effect of wind speed averaging time on the calculation of sand drift potential new scaling laws abstract drift potential dp is a key factor used to quantify aeolian sand transport and it is often used for predicting wind erosion and dune mobility under climate change scenarios it is proportional to the mean of the cube of the wind speed at a 10 m height when that wind speed is above 6 2 m s 12 knots a speed threshold above which sand can be transported by the wind dp depends on the temporal resolution and the averaging time of the wind velocity measurements usually either a 10 min or 1 h mean wind speed is used to calculate the dp although different studies have used different averaging periods for calculating the mean wind speed and consequently the dp here we perform a comprehensive analysis of an extensive long term wind speed database from different locations around the world and from reanalysis data sources and show that dp decreases with the averaging time of the wind speed the decrease of dp versus the averaging time interval can be approximated by a stretched exponential function in addition the relative decrease of dp as a function of the maximum dp is smaller for high wind speed sites this result is a consequence of the fact that high dp sites are characterized by longer clusters of successive wind speed events above the threshold velocity they are thus less affected by the time averaging process interestingly the clusters lengths decay exponentially with wind speed and faster for low dp sites our new results have important implications for calculating the effective dp and for better estimating the biases that result from using wind data with different averaging times which is a common problem in aeolian research we also found an approximate linear relation between dp and the wind power that is close to the analytic approximation for the relation between the two this new finding has many important applications since it will allow one to calculate dp from wind power data and vice versa in addition it implies that the same scaling laws found for dp also exist for the wind power

variation in grain size and morphology of an inland parabolic dune during the incipient phase of stabilization in the hobq desert china abstract a significant increase in rainfall in the summer of 2012 on the southern fringe of the hobq desert inner mongolia resulted in the vegetation and thus stability of dunes in this area our research focuses on a typical parabolic dune which was active in 2011 and became stabilized after vegetation colonization topographic surveys and surface sediment analysis of the morphology and surface sands of the parabolic dune indicate that decreasing mean grain size and sorting values better sorting slightly more positive skewness and increasing kurtosis occurred over the dune surface during the incipient phase of stabilization there was a strong relationship between grain size sorting and dune mobility surface sand from the stabilized dune was generally finer and better sorted than at the same location when the dune was active during 2011 2012 the dune head had moved eastwards by approximately 2 3 m while its two arms expanded outward by approximately 3 2 m the height of the dune decreased and the dune became larger with a decreasing volume once anchored 2013 2014 the overall morphology and the grain size and sorting characteristics of the dune became more constant and quite different than when the dune was active

contrasting styles of shelf sediment transport and deposition in a ramp margin setting related to relative sea level change and basin floor topography turonian cretaceous western interior of central utah usa abstract the turonian lower ferron sandstone and juana lopez members of the mancos shale in the western interior foreland basin form a series of regressive shoreface to shelf depositional complexes sourced from the sevier fold thrust belt to the west continuous dip parallel outcrop exposures around the northern and eastern edges of the tertiary san rafael anticline sra in central utah provide an insight into the origins of anomalous marine mudstone encased sandstones lower ferron strata consist of both coarsening and thickening upward and sharp based shoreface successions interpreted to have been deposited as sequential highstand and falling stage systems tracts overlying these shallow marine deposits is a surface that marks sediment bypass that is correlated down dip into coarse grained cross bedded sandstones interpreted as the deposits of channelised turbidity flows these turbidites are considered to be the products of sustained hyperpycnal flows exiting rejuvenated lowstand rivers based on sustained flow indicators such as dune scale cross bedding absence of genetically related slumps and delta front deposits in up dip areas surfaces of sediment bypass coarser grain sizes than the underlying shoreface deposits and regional palaeogeography the flows are interpreted to have been ignitive in proximal areas down a tectonically induced slope in the uplifted area of the farnham dome the change in depositional style from falling stage to lowstand systems tracts is attributed to increased rates of sediment supply to the shoreline promoting hyperpycnal flows a flooding surface caps the interval and separates the lower ferron sandstone from the overlying juana lopez member this interval in contrast consists only of heterolithic parallel and ripple laminated graded sandstone mudstone couplets interpreted to have been deposited by turbulent storm induced geostrophic flows the couplets are arranged into bundles and are interpreted as parasequences which in turn are arranged into a progradational parasequence set deposited during a period of sea level highstand divergent sole mark and bedform palaeocurrents from both members suggest slight eastward deflection of the turbulent flows off the proto sra further evidence for this topography is inferred from an absence of turbidites along the western side of the structure the inferred influence of local basin floor structures on sedimentation of these units has important implications for structural models for this basin for generalized sequence stratigraphic models applied to ramp type foreland basin sequences and for elucidating the origin of anomalous marine mudstone encased sandstone bodies

using fire scars and growth release in subfossil scots pine to reconstruct prehistoric fires abstract fire scars indicating low to moderate intensity fires on peat deposits have been sampled from subfossil scots pine pinus sylvestris l at sites in england wales and south west ireland analysis of ring width responses to one fire event in 2800 bc illustrates its rejuvenating effect on pinus sylvestris woodland supporting a growing body of modern and palaeoecological data that illustrates the regenerative role played by fire in persistence of pinus sylvestris woodland both the scale and timing of these fires suggest that infrequent low to moderate intensity fires are sufficient to stimulate pinus sylvestris growth this effect is shown by average increases in ring width following the fire of between 0 62 and 1 16 mm in non scarred trees and between 0 92 and 2 74 mm in fire scarred individuals growth release in non scarred trees may prove to be a more reliable method of detecting fire than using the relatively rare fire scars alone radii at time of scarring varied between 1 85 and 11 2 cm much smaller than is predicted to survive from modern studies

initiation and early development of barchan dunes a case study of the moroccan atlantic sahara desert abstract this paper describes field measurements that document the formation of barchan dunes in the moroccan atlantic sahara desert the first mechanism described is the transformation of patches and proto dunes at cap juby beach to barchan dunes of elementary size this transformation is discussed in relation to the wind speed and saturation length the second mechanism is the ejection of small barchans of elementary size by other small barchans in response to the perturbation of the target barchan by two other impacting small barchans this remote initiation is discussed in relation to the bulk flux transported by the barchan dunes involved in this interaction and to their morphology other modes of barchan initiation observed in the field are also presented

aeolian granule ripple deposits namibia granule ripples are a common feature of most dunefields yet they have seldom been recognized in ancient deposits although granule ripples are common in erosional settings such as windward slopes of dunes or scour surfaces in interdunes they nevertheless migrate laterally and leave distinctive deposits that can be recognized in ancient rocks these deposits have characteristics of type b sand sheet deposits including poured in texture curving ripple trough tangential coarse grained foresets irregular silty layers well sorted coarse and fine layers either horizontal or within foresets and fine layers in ripple troughs wind tunnel experiments suggest that under low velocity wind conditions granule ripples grow to a significant degree as parasites dependent on saltation of fine sand grains whose impact moves the larger grains of the granule ripple although the depositional surface of granule ripples is commonly coated with a layer of coarse grains this is in most places only a few grains thick underlying deposits commonly have a poorly sorted or poured in texture this texture results from an admixture of fine grains that fall among the spaces between the larger grains during deposition

coarse aeolianites sand sheets and zibar interzibar facies from the mesoproterozoic cuddapah basin india abstract the mesoproterozoic arenaceous successions of the egalapenta member cuddapah basin india are regionally developed and cover hundreds of square kilometers in and around the krishna gorge near the northern limit of the basin they are dominated by aeolian sand sheets major facies attributes of the aeolian sandsheets are coarse grained low relief bedforms with packages of wind ripple laminae that constitute the zibar facies and medium to coarse grained sandstones with bundles of wind ripple laminae that represent the interzibar deposits depending on the angle of climb and migration the zibars and interzibars produced two depositional successions which include an amalgamated interzibar facies devoid of zibars and an interbedded zibar interzibar facies in addition other attributes include low angle cross stratification coarse grained high index ripple lamination gently dipping irregular erosional surfaces and normal to inversely graded horizontal lamination fine to medium grained sandstones with high angle cross stratification represent the dune facies which are interstratified with the sandsheets these are associated with calcareous mudstone sandstones forming the sabkha facies and the laminated tabular cross stratified channelised fine to coarse grained sandstones representing the ephemeral fluvial deposits extensive outcrops of the egalapenta member bear strong signatures of aeolian dune interdune facies sand sheets with zibar and interzibar deposits have been considered as marginal erg facies

deltaic coals of ferron sandstone member of mancos shale predictive model for cretaceous coal bearing strata of western interior the upper cretaceous ferron sandstone member of the mancos shale the coal bearing unit of the emery coalfield in central utah shows accumulation of clastic sediments in a lobate river dominated deltaic system that existed along the western shoreline of the interior cretaceous seaway during late turonian time five cycles of deltaic sedimentation each containing one major coal bed or coal zone are represented a clear genetic relationship exists between the geometries of the major coal beds of the emery field and the geometries of the delta front sandstone units with which they are associated the thicker part of each coal bed extends from the vicinity of the landward pinch out of the associated delta front sandstone landward to a distance of about 10 km this genetic relation forms the basis of a predictive model that can be used in designing more cost effective exploration programs in coal bearing strata of cretaceous age in the western interior

dunes on the skeleton coast namibia south west africa geomorphology and grain size relationships simple and locally compound transverse and barchanoid dunes dominate the 2000 km2 skeleton coast dunefield in northwestern namibia south west africa dune height and spacing are closely correlated r 0 89 and decrease across the dunefield from southwest to northeast with an accompanying change from transverse to barchanoid ridges and ultimately barchans the dunes are aligned transverse to the dominant strong south and south southwest onshore winds alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune forming winds to swing to the right over the dunes but resume their original direction beyond grain size and sorting vary at three scales the dune the dune landscape and through the dunefield overall the sands derived from three localities by deflation from beaches supplied by vigorous longshore drift become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing a statistically significant relationship r 0 65 was established between dune spacing and the phi grain size of the coarser fraction of the dune sands demonstrating the importance of the protective effects of coarse grains and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand

dynamic processes acting on a longitudinal seif sand dune abstract field measurements were made on a longitudinal dune in the sinai desert in order to understand its morphology and dynamics the field measurements contradicted the wind structure indicated by the helicoidal flow theory rather it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank the essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line the occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line when this angle is 40 the velocity of the deflected wind drops and deposition takes place on the lee flank the angle of incidence in each wind storm is changed intermittently between 30 and 100 along the dune because the dune meanders and because of the sinuous outline of the crest line in this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line as a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month peaks and saddles along the crest line advance at an average rate of 0 7 m per month the lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition this can explain the formation of peaks along the crest line of the dune

thermogenic and secondary biogenic gases san juan basin colorado and new mexico implications for coalbed gas producibility the san juan basin is the most prolific coalbed gas basin in the world with 1992 production exceeding 440 gcf footnote 12 4 billion m3 resources of approximately 50 tcf 1 4 trillion m3 and proved reserves of over 6 tcf 170 billion m3 coalbed gas wells with the highest production initial potential greater than 10 mcf day or 0 28 million m3 day occur in the overpressured north central part of the basin hydrologic analysis indicates that overpressure in the fruitland formation is artesian in origin and represents repressuring that developed during the middle pliocene highly permeable laterally continuous coal beds override abandoned shoreline pictured cliffs sandstones and extend to the elevated recharge area in he northern basin to form a dynamic regionally interconnected aquifer system coal rank and basin hydrodynamics control the composition of fruitland coalbed gases which varies significantly across the basin chemically dry gases in the north central part of the basin coincide with meteoric recharge and regional overpressure the consistency of methane dgr13c values across the basin the presence of isotopically heavy carbon dioxide in coalbed gases and bicarbonate in formation waters and biodegraded n alkane distributions of some coal extracts indicate that coalbed gases in the north central basin are a mixture of thermogenic 25 50 secondary biogenic 15 30 and migrated thermogenic 12 60 gases migrated conventionally and hydrodynamically trapped gases in situ generated secondary biogenic gases and solution gases result in gas content that plot on or above the coal sorption isotherm bacteria transported basinward in groundwater flowing from the elevated northern basin margins metabolized wet gas components n alkanes and organic compounds in the coal and generated secondary biogenic methane and carbon dioxide subsequent to coalification uplift erosion and cooling these gases may be limited to basin margins where shallow depths and structural deformation result in higher permeability or may extend more than 35 mi 56 km basinward from the recharge zone the presence of appreciable secondary biogenic gas indicates an active dynamic flow system with overall permeability sufficient for high productivity basin hydrogeology reservoir heterogeneity location of permeability barriers no flow boundaries and the timing of biogenic gas generation and trap devel pment are critical for exploration and development of unconventional gas resources in organic rich rocks

evaluation of undiscovered natural gas in the upper cretaceous ferron coal wasatch plateau total petroleum system wasatch plateau and castle valley utah abstract the total petroleum system approach was used to estimate undiscovered gas potential of the wasatch plateau and castle valley central utah the ferron coal wasatch plateau total petroleum system was geologically defined and subdivided into seven assessment units six of which were formally evaluated geologic data considered in defining the assessment unit boundaries included thermal maturity coal presence and thickness overburden thickness and faulting intensity historical production data were also used to estimate volumes of gas from undrilled areas the one conventional assessment unit includes almost the entire area of the petroleum system and is characterized by known accumulations that occur in structural or combination traps in sandstone reservoirs the estimated undiscovered conventional producible gas that may be added to reserves of this unit ranges from a low f95 of 14 8 billion cubic feet bcfg 419 million cubic meters mm 3 of gas to a high f5 of 82 bcfg 2321 mm 3 and a mean value of 39 9 bcfg 1130 mm 3 continuous gas accumulations are those in which the entire assessment unit is considered to be gas charged within these assessment units there may be wells drilled that are not economic successes but all are expected to contain gas coalbed gas is in this continuous category mean estimates of undiscovered gas for the five continuous assessment units are 1 northern coal fairway drunkards wash 752 3 bcfg 21 323 mm 3 2 central coal fairway buzzard bench 536 7 bcfg 15 194 mm 3 3 southern coal fairway 152 6 bcfg 4320 mm 3 4 deep 6000 feet plus coal and sandstone 59 1 bcfg 1673 mm 3 5 southern coal outcrop 10 6 bcfg 300 mm 3 and joes valley and musinia grabens not assessed the mean estimate of undiscovered gas for the entire tps is 1551 2 bcfg 43 914 mm 3 there is a 95 chance that at least 855 7 bcfg 24 225 mm 3 and a 5 chance that at least 2504 bcfg 70 888 mm 3 of undiscovered producible gas remain in the tps

the use of mineral magnetism in the reconstruction of fire history a case study from lago di origlio swiss alps abstract the use of magnetic measurements in the detection of fire signals has been neglected since the work of rummery et al 1979 yet considerable developments have been made in the interpretation of magnetic measurements over the last 16 years this paper presents a study of the fire history of lago di origlio in the southern swiss alps the study utilises the technique of mineral magnetism alongside the stratigraphic pollen spore and charcoal records correlation between the various proxy records indicates that a magnetic fire record is present within the sediments for the last 4 ka the magnetic fire record has a distinct mineralogical and magnetic grain size signature that can be recognised against the background sedimentary signal the results suggest that magnetic measurements may be usefully employed in the reconstruction of fire history their application is rapid and non destructive and the results may provide additional information in relation to the links between catchment fire events and the sedimentary record

measurements of the aeolian sand transport saturation length the wavelength at which a dune pattern emerges from a flat sand bed is controlled by the sediment transport saturation length which is the length needed for the sand flux to adapt to a change in wind strength the influence of the wind shear velocity on this saturation length and on the subsequent dune initial wavelength has remained controversial in this paper we present direct measurements of the saturation length performed in a wind tunnel experiment complementary to this initial dune wavelengths are measured under different wind conditions in particular after storms using the linear stability analysis of dune formation it is then possible to deduce the saturation length from field data both direct and indirect measurements agree that the saturation length is almost independent of the wind strength this result supports the idea that grain inertia is the dominant dynamical mechanism limiting sediment transport saturation on dunes

geomorphology and origin of yardangs in the kumtagh desert northwest china yardangs are typical wind eroded landforms that are found in most of the world s major deserts this paper describes the morphology of yardangs in the kumtagh desert analyzes their control factors and discusses their development processes age and rates of formation yardangs in the kumtagh desert lack the ideal streamlined morphology and the length to width ratio close to 4 1 that have been previously described as being due to their unique controlling factors which include a combination of stratigraphic structures wind erosion and fluvial erosion fluvial erosion plays a particularly important role in the development of the yardangs though wind continuously sculpts their morphology the development of yardangs can be divided into four stages an embryonic stage adolescence maturation and recession most yardangs in the kumtagh desert are in the mature to receding stages we determined an approximate age for the yardangs based on the erosion rates estimated by several researchers on this basis the yardangs in the kumtagh desert appear to have formed during the holocene

slipfaceless whaleback dunes in a polar desert victoria valley antarctica insights from ground penetrating radar the lower victoria valley is one of the mcmurdo dry valleys antarctica and has the largest concentration of aeolian sand dunes on the continent aeolian bedforms include elongate slipfaceless dunes which have been called whaleback dunes these dunes are composed of coarse sand and capped by granule ripples ground penetrating radar gpr profiles across one of these dunes reveal low angle inclined sigmoid tangential and convex reflections that are interpreted as strata within the dune these dipping strata record the migration of the whaleback dune and show that they are not sand mantles as previously described but are actively migrating long wavelength low amplitude bedforms resembling zibar an 800 m profile along the axis of the dune reveals low angle dips from west to east showing that the dune has accreted towards the east gpr profiles collected at 100 m intervals transverse to the dune axis reveal sets of cross stratification dipping towards the south at the eastern end of the dune and towards the north at its western end these apparent dips are resolved to show that the dune has migrated from west to east driven by westerly foehn winds and katabatic winds blowing from the polar ice cap whilst at the same time it has been building obliquely towards the south accretion towards the north at the western end of the dune is attributed to reworking of the dune sand by easterly winds blowing inland from mcmurdo sound an unconformity within the dune suggests that the wind regime has varied in the past beneath the unconformity the direction of dune migration was from west to east and eastward extension of the dune continues at the present day however this is combined with accretion towards the north and west at the western end of the dune which is not recorded in the older sediments beneath the unconformity sand wedge structures that may have taken hundreds to thousands of years to form are found within the dune and suggest that arid conditions suitable for dune construction have persisted in victoria valley for a considerable time

neolithic population crash in northwest europe associated with agricultural crisis the focus of this paper is the neolithic of northwest europe where a rapid growth in population between 5950 and 5550 cal yr bp is followed by a decline that lasted until 4950 cal yr bp the timing of the increase in population density correlates with the local appearance of farming and is attributed to the advantageous effects of agriculture however the subsequent population decline has yet to be satisfactorily explained one possible explanation is the reduction in yields in neolithic cereal based agriculture due to worsening climatic conditions the suggestion of a correlation between neolithic climate deterioration agricultural productivity and a decrease in population requires testing for northwestern europe data for our analyses were collected during the cultural evolution of neolithic europe project we assess the correlation between agricultural productivity and population densities in the neolithic of northwest europe by examining the changing frequencies of crop and weed taxa before during and after the population boom and bust we show that the period of population decline is coincidental with a decrease in cereal production linked to a shift towards less fertile soils

winds and sand movements in the namib sand sea wind regimes in the vicinity of the namib sand sea are high energy unimodal near the coast becoming bimodal or complex inland there is an overall decrease in wind energy and sand transport rates from south to north and west to east such that sand moves from coastal and southern source areas to accumulate in the northern and central parts of the sand sea such a pattern can explain much of the observed spatial variability in dune types sizes and sediment characteristics and lends support to a climatic model of sand sea formation in this region seasonal and daily cycles of wind velocity and direction give rise to episodic sand transport most of which is generated by winds of moderate velocity and frequency

climbing zibars of the algodones abstract zibars are coarse grained low relief slipfaceless eolian bedforms that occur on sand sheets and within interdune corridors of many eolian sand seas zibar surface features consist exclusively of wind ripples and local shadow and shrub coppice dunes associated with vegetation a study of zibars located on the southwestern margin of the algodones dune field california shows that zibars and their associated interzibar areas are migrating features oriented transverse to oblique to the resultant sand transport direction zibars leave deposits formed by deposition on the zibar lee face the zibar shape modifies the near surface airflow to produce a subtle grain size change across the zibar interzibar surface flow expansion not separation leeward of the zibar crest causes the lee face deposits those preserved upon bedform migration to have the finest grain size on the zibar interzibar surface sediment coarser than that deposited on the zibar lee face is transported more slowly and less frequently and thus becomes concentrated on the zibar stoss slope and ultimately becomes interzibar deposits migration of zibars and interzibar areas can produce two characteristic depositional sequences depending upon the angle of climb for low angles of climb a sequence of stacked amalgamated interzibar deposits is preserved zibar deposits are absent amalgamated interzibar deposits consist of low angle usually less than 5 wind ripple laminae of medium to coarse sand given higher angles of climb deposits of both the entire interzibar and zibar lower lee face are preserved low angle interzibar deposits of medium to coarse sand are overlain tangentially by finer grained fine to medium sand wind ripple laminae dipping less than 15 of the zibar lee face lee face wind ripple laminae are sharply truncated and overlain by the succeeding set of interzibar wind ripple deposits this zibar interzibar sequence is distinctive and allows for the detailed interpretation of some ancient sand sheet deposits as left by migrating zibars a possible example of ancient zibar deposits is present in the entrada sandstone jurassic of southwestern colorado

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

production waters associated with the ferron coalbed methane fields central utah chemical and isotopic composition and volumes this study investigated the composition of water co produced with coalbed methane cbm from the upper cretaceous ferron sandstone member of the mancos shale in east central utah to better understand coalbed methane reservoirs the ferron coalbed methane play currently has more than 600 wells producing an average of 240 bbl day well water water samples collected from 28 wellheads in three fields buzzards bench drunkards wash and helper state of the northeast southwest trending play were analyzed for chemical and stable isotopic composition water produced from coalbed methane wells is a na cl hco3 type water from the drunkards wash field has the lowest total dissolved solids tds 6300 mg l increasing in value to the southeast and northeast in the helper state field about 6 miles northeast water has the highest total dissolved solids 43 000 mg l and major ion abundance indicates the possible influence of evaporite dissolution or mixing with a saline brine in the southern buzzards bench field water has variable total dissolved solids that are not correlated with depth or spatial distance significant differences in the relative compositions are present between the three fields implying varying origins of solutes and or different water rock interactions along multiple flow paths stable isotopic values of water from the ferron range from 0 9 to 11 4 18o and 32 to 90 2h and plot below the global meteoric water line gmwl on a line near but above values of present day meteoric water isotopic values of ferron water are consistent with modification of meteoric water along a flow path by mixing with an evolved seawater brine and or interaction with carbonate minerals analysis of isotopic values versus chloride conservative element and total dissolved solids concentrations indicates that recharge water in the buzzards bench area is distinct from recharge water in drunkards wash and is about 3 c warmer these variations in isotopes along with compositional variations imply that the ferron reservoir is heterogeneous and compartmentalized and that multiple flow paths may exist

suppressed vitrinite reflectance in the ferron coalbed gas fairway central utah possible influence of overpressure chemical and thermoplastic properties of coals in the ferron coalbed methane fairway indicate that coals in the north are of higher rank than coals in the south measured vitrinite reflectance does not accurately show this variation of coal rank although vitrinite reflectance in the southern and central part of the fairway is consistent with other measures of coal rank suppressed vitrinite reflectance is observed in the north where methane contents are relatively high this coincidence of suppressed reflectance and relatively high coalbed methane yields may be significant we speculate that the suppressed reflectance values result from a burial history where overpressure developed during the early stages of coalification and persisted until recent uplift and cooling such instances may be diagnostic of prospective coalbed methane targets elsewhere

granule ripples in the kumtagh desert china morphology grain size and influencing factors granule ripples are found mainly in four regions of the kumtagh desert in china they are characterized by an asymmetrical shape with gentle lower slopes on both sides and abrupt crests the ripples tend to be oriented perpendicular to the prevailing winds except when they form near obstacles such as yardangs the wavelengths range between 0 31 m and 26 m and heights h range from 0 015 m to 1 m the relationship between wavelength and height can be described by a simple linear function and the mean ripple index h is about 20 4 for the study sites the sediments are poorly sorted with negative to very negative skewness at lee and stoss slopes and between ripple troughs which confirms the poured in and shadow appearance described by previous researchers the bimodal or trimodal distributions of grains with modes of 1 16 0 5 and 3 16 and the enrichment of coarse particles at the ripple surface with coarse granule contents ranging between 5 2 and 62 1 indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes although the impact of saltating particles and consequently the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro scale however the characteristics of local sediments wind regimes and topographical obstacles as well as the feedbacks among bedform and airflow more strongly affect the development and alignment of granule ripples at a macro scale

texture and composition of titan s equatorial sand seas inferred from cassini sar data implications for aeolian transport and dune morphodynamics the texture composition and morphology of dunes observed in the equatorial regions of titan may reflect present and or past climatic conditions determining the physio chemical properties and the morphodynamics of titan s dunes is therefore essential to understanding of the climatic and geological history of the largest moon of saturn we quantitatively derived average surface properties of dune and interdune areas texture composition from modeling of the microwave backscattered signal and monte carlo inversion of the despeckled cassini sar data over titan s three largest sand seas belet shangri la and fensal we present the first analysis of the backscatter functions extracted from despeckled sar images that cover such a large range in incidence angles including data from the beginning of the cassini mission up to its grand finale we show that dunes and interdunes have significantly different physical properties dunes are found to be more microwave absorbent than interdunes additionally potential secondary bedforms such as ripples and avalanches may have been detected providing potential evidence for currently active dunes and sediment transport our modelling shows that the interdunes have multi scale roughnesses with higher dielectric constants than the dunes which have a low dielectric constant consistent with organic sand the radar brightness of the interdunes can be explained by the presence of a shallow layer of significantly larger organic grains possibly non mobilized by the winds together our findings suggest that titan s sand seas evolve under the current multi directional wind regimes with dunes that elongate with their crests aligned in the residual drift direction

the reconstruction of boreal forest fire history from lake sediments a comparison of charcoal pollen sedimentological and geochemical indices abstract fossil charcoal fossil pollen sedimentological and geochemical analyses of lake sediments have been used previously to reconstruct a history of local fires and resulting vegetation change the rationale behind these approaches is described and the usefulness of each technique for reconstructing fire history in the boreal forest is assessed empirically historical and dendrochronological records provide regional and local fire histories for a site in wood buffalo national park alberta canada the local and regional history of fires is compared with the microscopic charcoal content macroscopic charcoal content elemental carbon content fossil pollen content sedimentology and geochemistry of annually laminated sediments from a small lake there is no significant correlation between the abundance of microscopic charcoal macroscopic charcoal and total elemental carbon content of the sediments automated measures of microscopic charcoal abundance made with an image analysis system are correlated significantly with optical counts of microscopic charcoal none of the charcoal measures provide unequivocal records of local fire activity and the abundance of microscopic charcoal appears to be influenced by variations in regional fire activity however the highest depositional rate of macrofossil charcoal occurred during the time of a fire that burned within the drainage basin variations in sedimentological measures and geochemistry do not correlate with local fire activity fossil pollen percentages and accumulation rates display a pattern of variation that is consistent with observed vegetation responses to fire in the boreal forest what is likely apparent in the pollen record are the results of a series of burns of sufficient extent and intensity to kill most of the above ground biomass of the vegetation in an area at least as great as the drainage basin the inability of evidence from lake sediments to provide detailed histories of past fire activity is not surprising given the wide range of variation in the spatial extent proximity intensity and impact of individual fires

time series and postglacial forest ecology abstract forest ecology suffers from a lack of long term community records preserved pollen data are richer in such information than is generally realized by applying suitable statistical techniques to pollen records one can learn much about competition succession and population dynamics in past tree communities in this study preserved pollen records from everitt lake nova scotia are analyzed as time series time domain studies reveal the post fire responses of individual tree taxa correlograms yield models of past forest succession patterns the models explain some effects of changing fire frequency thus suggesting mechanisms by which fire competition and climate combine to produce long term forest composition changes frequency domain studies suggest relationships between disturbance cycles stand composition and forest mosaics fire frequencies are seen to be highest where fire dependent species abound and most regular where tree stands have uniform not mixed composition

drunkard s wash unit coalbed methane production from ferron coals in east central utah the drunkard s wash project produces dry coalbed methane gas from coals within the ferron sandstone member of the mancos shale the project covers 120 000 acres on the western flank of the san rafael uplift in east central utah gas was first produced into the sales line in january 1993 the field is being developed on 160 acre spacing with 73 wells currently producing 32 2 mmcfd for an average of 437 mcfd well thirty three of those wells have been producing for 32 months and now average 637 mcfd well most of the wells show a classic coalbed methane negative decline curve with increasing gas rates as the reservoir pressure declines due to production of water daily water production is 14 500 bpd for an average of 199 bwpd well total coal thickness ranges from 7 ft to 48 ft with an average of 24 ft the coals occur in 3 to 6 seams at depths of 1350 to 2450 ft the coal rank is high volatile a b bituminous we can not yet see a correlation between total coal thickness and current production all wells are cased and hydraulically stimulated and most require pumping units to handle the large volumes of water however 22 wells domore not require pumps and flow unassisted to the surface the structure consists of monoclinal westward dip a thin tonstein layer in the bottom coal seam serves as an excellent datum for mapping enhanced production is encountered along a southwest plunging nose that probably formed additional fracture permeability within the coals northeast trending reverse faults with small displacement appear to compartmentalize the reservoir the ferron coals were deposited in a river dominated deltaic system that prograded to the east and southeast during turonian coniacian upper cretaceous time the ferron sandstone member represents an eastward thinning elastic wedge that was deposited during regression of the western interior cretaceous seaway less

the dominant processes of sediment distribution and focusing in a small eutrophic monomictic lake there is evidence for 10 mechanisms of sediment distribution in small lakes the sediment accumulation rates measured from a common horizon in cores from 64 sites on esthwaite water u k were used to determine the relative importance of these mechanisms on the distribution of sediment in the lake river inflows generally produced localized effects but there were indications of periodic turbidity flows to the deepest point of the lake from the major inflow active sediment focusing processes were the dominant distribution mechanisms a major resuspension of sediment at autumn overturn probably being the most important the remaining variance was much greater than observed in similar work elsewhere suggesting that redistribution of sediment by direct and indirect wave action may be taking placeall over the lakebcd during isothermal periods the relative contributions of the different processes were corroborated by analysis of previously published sediment trap data

the role of streamline curvature in sand dune dynamics evidence from field and wind tunnel measurements abstract field measurements on an unvegetated 10 m high barchan dune in oman are compared with measurements over a 1 200 scale fixed model in a wind tunnel both the field and wind tunnel data demonstrate similar patterns of wind and shear velocity over the dune confirming significant flow deceleration upwind of and at the toe of the dune acceleration of flow up the windward slope and deceleration between the crest and brink this pattern including the widely reported upwind reduction in shear velocity reflects observations of previous studies such a reduction in shear velocity upwind of the dune should result in a reduction in sand transport and subsequent sand deposition this is not observed in the field wind tunnel modelling using a near surface pulse wire probe suggests that the field method of shear velocity derivation is inadequate the wind tunnel results exhibit no reduction in shear velocity upwind of or at the toe of the dune evidence provided by reynolds stress profiles and turbulence intensities measured in the wind tunnel suggest that this maintenance of upwind shear stress may be a result of concave unstable streamline curvature these additional surface stresses are not recorded by the techniques used in the field measurements using the occurrence of streamline curvature as a starting point a new 2 d model of dune dynamics is deduced this model relies on the establishment of an equilibrium between windward slope morphology surface stresses induced by streamline curvature and streamwise acceleration adopting the criteria that concave streamline curvature and streamwise acceleration both increase surface shear stress whereas convex streamline curvature and deceleration have the opposite effect the relationships between form and process are investigated in each of three morphologically distinct zones the upwind interdune and concave toe region of the dune the convex portion of the windward slope and the crest brink region the applicability of the model is supported by measurements of the rate of sand transport and the change of the dune surface in the field

fluvial sequence stratigraphy the wapiti formation west central alberta canada abstract outcrop exposures and high resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the campanian maastrichtian wapiti formation western interior foreland basin alberta canada this framework defines four unconformity bounded depositional sequences a d based on sequence stratigraphic methodology well log patterns and facies analysis in ascending order sequence a records the transition from the underlying marine facies of the puskwaskau formation into the wapiti fluvial facies and consists of strongly progradational and aggradational stacking patterns sequences b and c show a similar pattern of basal amalgamated channel fill deposits that grade upwards into floodplain dominated strata finally sequence d is dominated by channelized sediments and extensive overbank facies an aggradational stacking pattern suggests deposition under high accommodation conditions maximum flooding surfaces are interpreted within fine grained deposits in the upper portions of sequences c and d they are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline this study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream controlled fluvial realm furthermore the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine wapiti formation into depositional sequences and component systems tracts

storm controlled oblique dunes of the oregon coast the large mean height 25 m spacing 300 m relatively straight crested dunes of the central oregon coast migrate an average of 3 8 m yr toward an azimuth of 26 the dunes are transverse to the strong south southwesterly winter storm winds that are responsible for their basic form orientation and migration the dry moderate north northwesterly summer winds modify the dune form but not the dune trend comparison of the sand transport calculated from wind data and the transport measured from dune migration indicates that the actual transport by the wet southerly winds is only one third of the amount calculated assuming dry conditions the resultant vector mean transport rate as recalculated by comparison of the measured and initially calculated rates is 34 m 3 m yr toward an azimuth of 45 the dunes are thus oblique by our definition of an oblique dune angle between dune trend and resultant transport direction between 15 and 75 the internal structures of the dunes confirm northward migration during wet conditions evidence for deposition during wet conditions includes slipface deposits deformed mostly by sliding and various structures formed by the adhesion of sand grains to wet surfaces most summer deposits are not preserved but those on the basal apron the gentle north slope at the base of the winter slipface have a high preservation potential a depositional model based on dune climbing predicts that the preserved record of oblique dunes formed by an obtuse bimodal wind regime would consist of tabular sets of crossbeds in which the dip angles increase upward from the base of each set

upper cretaceous ferron sandstone major coalbed methane play in central utah recent drilling for coalbed gas in the upper cretaceous ferron sandstone member of central utah has resulted in one of the most successful plays of this kind exploration to date has resulted in three fields and a potential fairway 6 10 mi 10 16 km wide and 20 60 mi 32 96 km long corresponding to shallow coal occurrence at depths of about 1800 3500 ft 545 1060 m in the ferron a sequence of interbedded fluvial deltaic sandstone shale and coal in the lower part of the cretaceous mancos shale coalbed methane cbm reservoirs in this interval consist of thin to moderately thick 3 10 ft 1 3 m coal beds of relatively low rank high volatile b bituminous and variable gas content ranging from 100 scf ton or less in the south to as high as 500 600 scf ton in the north productive wells have averaged more than 500 mcf day and after several years continue to typically show negative production declines in the major productive area drunkards wash unit the first 33 producers averaged 974 mcf and 85 bbl of water per day after five years of continuous production estimated ultimate recoverable reserves for individual wells in this unit range from 1 5 to 4 bcf based on several criteria including gas content thermal maturity and chronostratigraphy the play is divided into northern and southern parts the northern part is characterized by coals that have the following characteristics 1 high gas contents 2 moderate thermal maturity e g vitrinite reflectance ro values of 0 6 0 8 3 good permeabilities 5 20 md 4 lack of exposure and 5 overpressuring due to artesian conditions southern coals have much lower average gas contents 100 scf ton and lower thermal maturity ro 0 4 0 6 and they are exposed along an extensive 35 mi 56 km outcrop belt that may have allowed a degree of flushing these coals however are also thicker and more extensive than those to the north and thus may retain significant begin page 200 potential northern coals appear to contain a mixture of gas from three sources in situ thermogenic methane migrated thermogenic methane from more mature sources and late stage biogenic gas current development is focused on the northern part of the stated fairway where well control and an existing infrastructure are present indications are that cbm exploration in the ferron will expand considerably in the near future

airflow reversal and alternating corkscrew vortices in foredune wake zones during perpendicular and oblique offshore winds on all sandy coastlines fringed by dunes understanding localised air flow allows us to examine the potential sand transfer between the beach and dunes by wind blown aeolian action traditional thinking into this phenomenon had previously included only onshore winds as effective drivers of this transfer recent research by the authors however has shown that offshore air flow too can contribute significantly through lee side back eddies to the overall windblown sediment budget to coastal dunes under rising sea levels and increased erosion scenarios this is an important process in any post storm recovery of sandy beaches until now though full visualisation in 3d of this newly recognised mechanism in offshore flows has not been achieved here we show for the first time this return flow eddy system using 3d computational fluid dynamics modelling and reveal the presence of complex corkscrew vortices and other phenomena the work highlights the importance of relatively small surface undulations in the dune crest which act to induce the spatial patterns of airflow and transport found on the adjacent beach

long term measurements of aeolian transport directional variations over a zibar surface in the northern kumtagh sand sea abstract zibars are aeolian bedforms created by armoring of the surface by coarse grains the existence and movement of these grains strongly influence zibar morphodynamics although aeolian sediment transport has been investigated for arid surface processes with a range of grain sizes the measurement durations were short making it difficult to establish the relationship between microscopic aeolian transport processes and macroscopic geomorphological processes in the present study we conducted field observations of aeolian sediment transport above a zibar in northern china s kumtagh sand sea with a segmented sand trap during six measurement periods throughout 2014 the sampler collected 314 76 kg of sediments within 1 m above the ground the directional variation indicated that about 52 5 of the sediments came from the north northeast and northwest the southeast provided the least sediments the strongest aeolian transport occurred between august and october the weakest was in winter the aeolian sediment flux decreased with height and 54 of particles were transported within 0 1 m above the ground the transport profiles fit an exponential decay function the flux s directional variation resulted from the combined effects of sediment availability and wind regime so the calculated net transport differed from the drift potential the seasonal and directional variations of aeolian transport significantly affect the morphodynamic process of zibars the trend and the internal sedimentary structure of zibars were closely related to the aeolian transport process

morphological and sedimentary features of oblique zibars in the kumtagh desert of northwestern china abstract zibars are coarse grain armored low relief aeolian bedforms with a large spacing but without slipfaces little is known of their morphodynamic processes even though they are ubiquitous at upwind desert margins in this paper we describe the morphological and sedimentary features of oblique zibars in the northeastern kumtagh desert of china analyze the effective wind regime and discuss the significance of the coarse grained sediments for zibar morphology and sedimentary structures due to a mantle of coarse grains oblique zibars and nearby linear dunes respond to different effective wind regimes that result in the angle between their geomorphological trends topographic surveys showed that the spacing of the oblique zibars ranged between 130 5 and 357 5 m and that the height ranged between 0 6 and 3 0 m the oblique zibar surface is almost entirely covered by coarse sand and includes gravel with a particle diameter of up to 2 34 the poorly sorted positively to very positively skewed surface sediments with mean grain size ranging between 0 2 and 1 5 were characterized by a bimodal distribution the spacing between the oblique zibars is closely related to the coarsest 5th percentile of the surface sediments and can potentially be explained by a combination of the saturation length and minimum dune size theories in addition the protectionist theory combined with the surface creep and vibration of coarse grains which allows infiltration of finer materials between the grains may account for the alternating coarse and fine laminae in the oblique zibars

the fire history of danish heathland areas as reflected by pollen and charred particles in lake sediments sediments deposited during the last 5400 years in two danish closed oligotrophic lakes have been analysed for pollen dark coloured hyphae and microscopic charred particles chronologies are provided by numerous radiocarbon datings redundancy analysis is used to develop a model for the relationship between concentrations of sedimentary charred particles and pollen at lake solso the only pollen type which is significantly correlated with charred particles is calluna the model is used to predict charred particle concentrations in the sediments of lake skanso from the calluna concentrations and the predicted values are compared to the observed the results indicate that 1 the source area and the means of transportation for microscopic charred particles and pollen are approximately identical 2 charred particles and pollen may be focused differentially in a lake and 3 high fire intensities triggered heathland expansion and heaths were maintained by fires through millennia

great sand sea and selima sand sheet eastern sahara geochronology of desertification the relation of playa sediments and associated archeological sites with longitudinal dunes allows estimation of ages for the two uppermost strata of the great sand sea active dune formation corresponds with interpluvial periods of hyperaridity dune stability corresponds with semiarid pluvial periods archeological sites associated with truncated paleosols in the selima sand sheet suggest a similar climatic relation and indicate that the isohyets of central sudan shifted at least 400 kilometers northward during the peak of pluvials

algodones dune field of southeastern california case history of a migrating modern dune field the algodones dune field of southeastern california is one of the largest active dune fields in north america the dune field is migrating in an easterly direction oblique to the resultant sand flow direction s 24 e the migration of the algodones results from an interaction between regional winds and the dune field this interaction generates a localized secondary flow that has caused the dune field to migrate in a direction oblique to the resultant sand flow direction four lines of evidence suggest that the algodones has migrated in an easterly direction 1 a ramp interpreted as the trailing edge of the dune field 35 m thick and 500 m wide composed of aeolian deposits that borders the western edge of the dune field no similar deposits are found on the eastern leading edge margin of the dune field 2 leading edge sand sheet deposits are exposed in interdune areas within the dune field these deposits are west of the modern leading edge sand sheet 3 across the breadth of the dune field sands are consistently coarser and more poorly sorted in the west and finer and better sorted in the east this observation suggests that sand is transported from west to east 4 eastward migration of a large compound complex crescentic dune if the dune field continues to migrate it will deposit a vertical sequence consisting of a basal sand sheet deposit consisting of wind and water ripple laminae small scale aeolian cross strata and ephemeral stream wadi deposits aeolian dune deposits consisting of medium scale aeolian compound cross strata small scale simple sets of aeolian cross strata with highly variable dip directions a sand sheet containing low angle wind ripple cross strata capped by a coarse sand lag super bounding surface

flow dynamics over a foredune at prince edward island canada time averaged windspeed profiles at eight locations over a relatively high 8 m vegetated topographically simple foredune were measured using cup and ultrasonic anemometry during an onshore wind event in may 2002 the experiment was part of a largerstudyonthesedimentarydynamicsofabeach dunecomplexinthegreenwichdunes princeedwardisland pei canada the foredune is vegetated with ammophila breviligulata and vegetation density ranged from 0 on the foredune ramp to upward of 70 at the dune crest topographic forcing and resulting flow acceleration was observed distinctly in windspeed profiles and linear speedup occurred for all elevations above the vegetation canopy a distinct inflection point is evident in normalized windspeed profiles over the dune indicating a net momentum sink below the vegetation canopy top and systematic speed down within the vegetation was observed up the foredune stoss slope wind speed profile structure was consistent for the range of incident wind speeds measured a comparison of normal and slightly oblique incident winds indicated that for similar approach winds wind speeds are consistently higher during oblique flow conditions the implications for foredune morphodynamics and sedimentation are discussed d 2004 elsevier b v all rights reserved

mid holocene charcoal stratigraphy fire history and palaeoecology at north gill north york moors uk abstract small peat mires are a favourable medium for the preservation of charcoal records that can be correlated more precisely with past fire history as part of multi proxy palaeoecological studies the north york moors upland has many suitable peat deposits with a well researched palaeoenvironmental history that offer the potential for high precision palaeofire studies we have examined the charcoal and pollen stratigraphy at the north gill site at a range of spatial and temporal resolutions for the mid holocene period between about 7k and 4 5k radiocarbon years ago in an individual core three size class charcoal records large small and microscopic reflect the scale and location of local fire events although the micro charcoal curve contains a background regional signal of about 10 of the charcoal pollen ratio most micro charcoal is generated locally and deposited close to its source at the site scale spatial comparison of four cores shows a variable relationship between tree pollen and micro charcoal concentrations which is an index of the size and intensity of local fire phases individual fires cannot be distinguished fine resolution sampling at the millimetre scale resolves major burning phases into discrete sub phases that may reflect the effects of individual fires at this fine temporal scale this multi scale research indicates that detailed charcoal stratigraphies at varying resolutions are capable of interpretation in terms of local regional and intermediate fire history