high angle wave instability and emergent shoreline shapes 2 wave climate analysis and comparisons to nature 1 recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms including capes flying spits and alongshore sand waves this instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle a maximum that occurs between 35 and 50 for several common alongshore sediment transport formulae here we introduce metrics that sum over records of wave data to quantify the long term stability of wave climates and to investigate how wave climates change along a coast for long point a flying spit on the north shore of lake erie canada wave climate metrics suggest that unstable waves have shaped the spit and furthermore that smaller scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable a shoreline aligned along the trend of the carolina capes united states would be dominated by high angle waves numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast local wave climates along these simulated capes and the carolina capes show similar trends shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability

sedimentary processes and the evolution of the distal bayside of long point lake erie long point spit on the north shore of lake erie is 40 km long and presently building into water that is 40 m deep annual sediment supply to the spit is estimated to be 1 0 106 m3 a 1 and is derived from the erosion of cohesive bluffs along more than 90 km of shoreline to the west the shoreline of the distal bayside consists of narrow barriers that connect the ends of dune ridges and enclose interdune ponds and swales unlike most barrier spits the distal end shows little evidence of the formation of dune recurves and the shoreline of the bayside rather than fronting a protected bay is exposed to waves generated by northeast winds blowing over a fetch 100 km results of wave refraction analysis indicate that because of the great depth of water at the tip there is almost no refraction of the dominant westerly and southwesterly waves around the distal end thus inhibiting the formation of recurves net sediment transport on the distal bayside is towards the distal end of the spit the result is

evaluation of simple geochemical indicators of aeolian sand provenance late quaternary dune fields of north america revisited abstract dune fields of quaternary age occupy large areas of the world s arid and semiarid regions despite this there has been surprisingly little work done on understanding dune sediment provenance in part because many techniques are time consuming prone to operator error experimental highly specialized expensive or require sophisticated instrumentation provenance of dune sand using k rb and k ba values in k feldspar in aeolian sands of the arid and semiarid regions of north america is tested here results indicate that k rb and k ba can distinguish different river sands that are sediment sources for dunes and dune fields themselves have distinctive k rb and k ba compositions over the basin and range and great plains regions of north america the hypothesized sediment sources of dune fields are reviewed and assessed using k rb and k ba values in dune sands and in hypothesized source sediments in some cases the origins of dunes assessed in this manner are consistent with previous studies and in others dune fields are found to have a more complex origin than previously thought use of k rb and k ba for provenance studies is a robust method that is inexpensive rapid and highly reproducible it exploits one of the most common minerals found in dune sand k feldspar the method avoids the problem of using simple concentrations of key elements that may be subject to interpretative bias due to changes in mineralogical maturity of quaternary dune fields that occur over time

infrared stimulated luminescence irsl dating of late holocene aeolian sands in the mojave desert california usa a new method of dating potassium feldspar grains from aeolian sands is demonstrated a luminescence signal is measured whilst the grains are stimulated in the near infrared at 880 nm a surface sand sample gave an age of 40 15 years showing that this method is able to provide ages for very young samples since the measurement of an infrared stimulated luminescence irsl signal can take place with a short infrared exposure the irsl signal of the grains is not depleted thus growth curves can be obtained for 5 mg sample aliquots this procedure was exploited in this paper dates were obtained for 10 samples from the kelso dune field as a demonstration of the applicability of the method in a desert environment where there is no material suitable for radiocarbon dating although the number of dates are limited sand from an area at the eastern end of the dune field with crescentic dunes showing a different wind direction from that of today had an age of 4115 335 years similar to the 3960 385 years fo

paleopedologic and geomorphic evidence for holocene climate variation shortgrass steppe colorado usa abstract radiocarbon dates of paleosols in northeastern colorado indicate distinct periods of stability and soil formation with intervening periods of instability resulting in soil truncation or burial a combination of pedologic and geomorphic indicators were used to resolve the duration of and prevailing climate during these periods five sites each having a paleosol were examined using both traditional soil analyses and grain size statistics the latter to decipher the mode of parent material deposition twenty local stream dune and bedrock deposits were analyzed using grain size statistics to establish benchmarks for comparison with soils field investigation supported by grain size frequency statistics indicate early holocene middle holocene and contemporary soils all formed in alluvium organic c and phytolith data suggest the early and middle holocene climatic conditions were more favorable for plant productivity than the present climate soil development in early and middle holocene paleosols suggests wetter soil moisture regimes than present low parent material carbonate contents suggest an eolian source for the carbonate in the bk and btk horizons the presence of paleosol btk horizons suggests a decrease in precipitation at the end of soil forming intervals followed by drought and subsequent soil burial

response of eolian geomorphic systems to minor climate change examples from the southern californian deserts abstract eolian processes and landforms are sensitive to changes in atmospheric parameters and surface conditions that affect sediment supply and mobility the response of eolian geomorphic systems to minor climate change can be examined through process response models based on a combination of relations between short term changes in climatic variables and eolian activity and the geologic and geomorphic record of holocene eolian activity at both time scales eolian activity in southern californian deserts is strongly controlled by variations in precipitation wind energy is not a limiting factor in this region formation of eolian deposits is a product of climatic changes that increase sediment supply from fluvial and lacustrine sources and may therefore be closely tied to periods of channel cutting and geomorphic instability during intervening periods eolian deposits migrate away from sediment source areas and are reworked modified and degraded remobilization of existing dormant dunes is a product of reduced vegetation cover and soil moisture in periods of drier climates the major control on these processes is decadal to annual changes in rainfall that determine vegetation cover and soil moisture content

migration and sedimentology of longshore sandwaves long point lake erie canada this paper describes the formation migration and sedimentology of sandwaves along the distal end of long point a 40 km long spit in lake erie some seven to nine sandwaves occur in a zone over the last 14 km of the spit they are characteristically 50 100 m wide at the downdrift end range in length from 350 m to 1500 m and migrate alongshore at rates that are typically 100 300 m year 1 measurements over a 7 year period show two forms of alongshore sandwave migration 1 a migratory jump and 2 downdrift accretion the migratory jump is commonly 200 500 m year 1 and results from the onshore migration and welding of an inner nearshore bar to the downdrift end of the sandwave this in turn leads to emergence of the bar over a distance of several hundred metres downdrift of the sandwave and isolation of the trough landward of the bar infilling of the trough abstracts large volumes of sediment from the local sediment transport system and may affect movement of the sandwave in the following year or movement of the next sandwave downdrift downdrift accretion commonly results in migration of 50 150 m year 1 and results from the refraction of waves around the distal end of the sandwave and episodic accretion of small swash bars this mechanism occurs less frequently and appears to reflect a local condition of lower sediment abundance often triggered by a large migratory jump in the previous year the process of bar emergence and infilling produces a distinct suite of sedimentary structures associated with the infilling of the landward trough and building of the sandwave berm the initial shoreline perturbation that generates the sandwave results from onshore migration and welding of inner nearshore bars and the development and growth of the sandwaves is promoted by refraction of highly oblique waves

emplacement of clay into sand by infiltration abstract laboratory experiments and examination of core samples from holocene sand bodies demonstrate that vadose infiltration of muddy water through sand is an effective mechanism by which clay can be emplaced into sand infiltrated clays form coatings on and bridges between sand sized framework grains clay particles are mostly oriented parallel to grain surfaces in coatings and perpendicular to grain surfaces in bridges the amount of clay emplaced as coatings and bridges is determined by complexly interacting variables that include sand grain size clay particle size clay particle shape concentration of suspended sediment and clay composition of these relatively coarse sand sizes and high concentrations of suspended sediment appear to promote the emplacement of the most infiltrated clay in holocene sands the formation of grain coatings and bridges is facies dependent infiltrated clays are most effectively emplaced in environments characterized by high suspended sediment concentrations fluctuating water levels and minimal sediment reworking e g point bar and delta plain in contrast virtually no infiltrated clay is emplaced in environments characterized by low suspended sediment concentration and continuous reworking e g beach and tidal delta

targeted control of sand hazards for a railway in extremely arid regions using fingerprinting approaches abstract reliable quantitative information on sediment sources is key for the reasonable arrangement of targeted measures that effectively control hazards of wind erosion along railways in extremely arid regions in northwest china the newly built golmud korla railway suffers from serious wind blown sand hazards which severely affect its future safe operation this study applied two frequently used fingerprinting methods optimum composite fingerprint and multiple composite fingerprint to quantitatively examine the contributions of different sediment sources to the railway in two typical areas research areas r1 and r2 the results revealed that nebkha was the main sediment source for the railway 46 5 in r1 followed by a dry playa 37 7 and sand dunes dune 1 15 8 in contrast sand dunes dune 2 were the main sediment source for the railway 75 2 in r2 followed by gobi 12 9 and a low lying coarse sand sheet lcss 11 9 according to the comprehensive assessment the sand fixing measure of spraying salt lake brine to form a crust for nebkha was recommended and the sand fixing measure of large vertical grids 15 m 15 m 1 5 m made of reed rod was suggested to control wind erosion of the dry playa near the railway and to trap the eroded sand from the upwind direction in r1 in r2 a small reed rod checkerboard barrier 1 m 1 m 0 2 m was suggested for dune 2 to effectively prohibit drifting sand from endangering the railway in addition this study also indicated that when two or more sediment sources have relatively similar properties the pairwise test to select tracers with significant differences between the two sediment sources would help reduce uncertainty which was recommended for similar studies in the future

large scale stabilized dunes on the high plains of colorado understanding the landscape response to holocene climates with the aid of images from space principal component analysis of landsat thematic mapper images from eastern colorado reveals stabilized dune fields that are composed of single and compound parabolic dunes some longer than 10 km these dunes have been reactivated at least four times in the past 10 000 yr at ca 9500 to 5500 yr b p 5500 to gt 4800 yr b p 4800 to gt 1000 yr b p and lt 1000 yr b p during droughts that probably exceeded the dry conditions during the 1930s dune orientations indicate that these landforms were molded by winds from the northwest which now dominate during the winter and spring with the passage of pacific air masses this study underscores the sensitivity of the landscape of the high plains to drought conditions which may become more prevalent because of the anticipated effects of greenhouse warming

experimental study of cut marks made with rocks unmodified by human flaking and its bearing on claims of 3 4 million year old butchery evidence from dikika ethiopia abstract in order to assess further the recent claims of 3 4 ma butchery marks on two fossil bones from the site of dikika ethiopia we broadened the actualistic interpretive zooarchaeological framework by conducting butchery experiments that utilized naive butchers and rocks unmodified by human flaking to deflesh chicken and sheep long limb bones it is claimed that the purported dikika cut marks present their unexpectedly atypical morphologies because they were produced by early hominins utilizing just such rocks the composition of the cut mark sample produced in our experiments is quite dissimilar to the sample of linear bone surface modifications preserved on the dikika fossils this finding substantiates and expands our earlier conclusion that considering the morphologies and patterns of the dikika bone surface modifications and the inferred coarse grained depositional context of the fossils on which they occur the dikika bone damage was caused incidentally by the movement of the fossils on and or within their depositional substrate s and not by early hominin butchery thus contrary to initial claims the dikika evidence does not warrant a major shift in our understanding of early hominin behavioral evolution with regard to carcass foraging and meat eating

spatial and temporal patterns of late quaternary eolian deposition eastern colorado u s a abstract eolian sediment covers about 60 of colorado east of the rocky mountains about 30 of the sediment is sand and 70 is loess initially flood plains were the principal sources of eolian sediment but during the holocene dunes formed from older eolian sand and alluvium on uplands since latest pleistocene time dominant dune forming winds have been northwesterly in the northern part of the region and southwesterly in the southern part at present sand sheets and dunes mainly parabolic types are stable and covered with vegetation in dunes sand is commonly 20 30 m thick but elsewhere averages

sand supply to the algodones dunefield south eastern california usa in an effort to gain a better understanding of the relationship between climate sand supply and aeolian sand deposition an investigation was undertaken in the algodones dunefield of south eastern california to determine 1 the source of the sand and 2 the mode of sand supply to the algodones dunefield textural geochemical and mineralogical analyses show that the dune sands were mainly derived from colorado river sands during episodes when the colorado river drained west to the salton basin instead of south to the gulf of california a model is presented which relates episodic aeolian deposition in the algodones dunefield to the growth of the resulting lake under a persistent intense north westerly wind regime and to subsequent desiccation of the lake following diversion of the colorado river to the gulf of california late holocene radiocarbon ages for relict lake shoreline deposits correlate with documented episodes of extreme flooding and increased winter storminess across the south western united states these conditions are likely to have been the cause of intensified north westerly winds which coincided with high stands of lake cahuilla although diversion of the colorado river to the salton basin occurred at least three times during the late holocene it is evident that the river did not change its course in response to the majority of the floods it appears that the critical control on diversion of the river was the difference in gradient between courses leading to the salton basin and gulf of california which in turn was influenced by fluvial deposition and tectonic activity flooding was able to cause diversion of the colorado river to the salton basin only when the difference in gradient between the two courses was relatively small

stratigraphic evidence for late quaternary dune activity near hudson on the piedmont of northern colorado stabilized dune fields are common features near hudson on the piedmont of northern colorado exposures in dune and interdune sites expose a sequence of eolian sediments and paleosols that record a complex history of eolian activity during the late quaternary radiocarbon and thermoluminescence age estimates on a horizons buried by eolian sand indicate that dunes were reactivated sometime between 7 and 9 ka on the basis of morphology of surface soils the dunes were most recently stabilized 3 ka at present there are no data to indicate if there were multiple periods of dune movement and stabilization during the holocene the penultimate pre holocene dune forming episode probably terminated ca 13 ka and may be coincident with the pinedale glaciation the stratigraphy at interdune sites shows at least two eolian depositional events prior to the penultimate event they were separated by periods of pedogenesis one of which may have exceeded 40 ka this analysis indicates that dunes in northern colorado were active during both cold arid and warm arid periods in the late quaternary

regional aridity in north america during the middle holocene increased aridity throughout the great plains and rocky mountain region during the middle holo cene has been documented from pollen records aeolian proxy variables in lake cores and active sand dune migration varve calibration provided by a continuously varved record of the holocene from a core from elk lake northwestern minnesota shows that the influx of aeolian clastic material increased beginning about 8 ka and ended about 3 8 ka with peak aeolian activity at about 6 ka if aeolian influx to elk lake corresponds in time to aeolian influx in other lakes and to maximum dune activity in minnesota dune fields then the varve calibration in elk lake provides precise time calibration of periods of peak aeolian activity in minnesota palaeowind studies from the minnesota dune fields show that the dominant wind direction when the dunes were active was from the northwest the same as the dominant wind direction in dune fields throughout the great plains and rocky mountains if the mid holocene aeolian act

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

stratigraphy and geochronology of upper quaternary eolian sand on the southern high plains of texas and new mexico united states eolian sand in dune fields and sand sheets cover 10 000 km 2 10 of the southern high plains of northwestern texas and eastern new mexico these deposits are concentrated in three west east trending belts of dunes the muleshoe lea yoakum and andrews dune fields from north to south that appear to be eastern extensions of the mescalero monahans dune system in the pecos river valley and in the seminole sand sheet a discontinuous accumulation of sheet sands between the lea yoakum and monahans andrews dunes the most common landforms are parabolic dunes associated with blowouts coppice dunes and sand sheets all typical of sandy vegetated semiarid landscapes barchan dunes in keeping with a relatively limited sand supply and an underlying surface that is relatively hard blackwater draw formation pleistocene and fence row dunes historic dunes formed along field boundaries these eolian deposits accumulated episodically in the late pleistocene and holocene and provide clues to the history of regional drought and aridity the earliest phase of sedimentation occurred when sheet sands were deposited between 11 000 and 8000 14 c yr b p probably in several phases based on archaeological data as a result of episodic drought beginning between 11 000 and 10 000 yr b p eolian deposits dating between 8000 and 3000 yr b p are rare although eolian sediment 8000 4500 14 c yr b p is ubiquitous in the draws that cross the region and paleoenvironmental indicators show that the region was subjected to aridity throughout middle holocene time the middle holocene deposits most likely were remobilized in late holocene time most of the deposits and landforms of the dune fields and sand sheets are late holocene dating before 4000 14 c yr b p and mostly before 1500 14 c yr b p the muleshoe and lea yoakum dunes and the seminole sand sheet underwent substantial eastward expansion in late holocene time buried soils and radiocarbon ages show that the eolian sand accumulated in several stages probably in response to cyclic drought the muleshoe dunes accumulated after ca 1300 cal yr b p ca 1400 14 c yr b p after ca 750 670 cal yr b p ca 850 750 14 c yr b p just after ca 500 cal yr b p ca 450 14 c yr b p and during the nineteenth and twentieth centuries the lea yoakum dunes were active after ca 3400 cal yr b p ca 3200 14 c yr b p and historically the seminole sand sheet was active ca 430 330 cal yr b p ca 360 14 c yr b p and in the twentieth century the andrews dunes were subjected to at least two phases of eolian sedimentation after ca 2320 cal yr b p ca 2320 14 c yr b p comparisons with eolian chronologies from other regions on the great plains suggest that dune mobilization was a regional phenomenon after ca 2300 cal yr b p ca 2300 14 c yr b p after ca 1500 1400 cal yr b p ca 1650 1550 14 c yr b p after ca 700 cal yr b p ca 800 14 c yr b p between 500 and 300 cal yr b p ca 450 300 14 c yr b p and in the nineteenth century the climatic fluctuations responsible for mobilizing the dunes probably were relatively minor yet the landscape impacts were substantial resulting in widespread wind erosion and dune construction

fish bones cut marks and burial implications for taphonomy and faunal analysis willis et al 2008 demonstrated that butchering fish can result in upwards of 500 cut marks per fish skeleton however despite various ethnographic studies that describe fish butchering techniques for consumption and drying cut marks are rarely observed or described for fish bone from archaeological sites to test the discrepancy between the experimental results and archaeological observations we buried 13 butchered fish skeletons for 27 months to observe whether the cut marks are still visible after exposure to post depositional taphonomic processes after burial we observed a general decrease up to 76 depending on the species of fish in the number of cut marks visible on fish bone accompanied by a shift from cut marks on identifiable elements to cut marks on unidentifiable bones and bone fragments these results impact the methods for analyzing archaeological fish bone and contribute to our understanding and interpretation of taphonomy aquatic faunal assemblages and prehistoric butchering practices

modern and late holocene wind regimes over the great plains central u s a the great plains of the central united states contain numerous presently stabilized dune fields that were active during the late holocene the most recent period of reactivation occurred about 700 1000 years ago during the medieval climatic anomaly a period of frequent severe drought recognized throughout the north american west dune orientations and internal bedding preserve information about paleowinds from this time period we compared paleowind information with modern winds and potential sand transport analyzed from meteorological data while both reconstructed paleowinds and modern winds include a strong northwesterly component over the northern to central portions of the great plains a significant difference exists to the south during the late holocene southwesterly winds had a strong influence on dune forms over the central and southern great plains while modern potential sand transport is dominated by southerly to southeasterly winds that bring moisture to the region from the gulf of mexico hypothetical dune types forming under modern winds would be different and have different crestal orientations than those preserved from the late holocene in order for such a shift in southerly winds to take place it is likely that 1 the typical position of the bermuda high in summer was shifted either to the east or to the south resulting in weaker low level winds from the south and southeast and greater extent of southwesterly winds on the great plains and or 2 drought likely enhanced by evapotranspiration and soil moisture feedbacks brought the normally higher level southwesterly flow down to the land surface given our understanding of megadroughts over the great plains as well as recent climate predictions for increased warmth and drought over this area future reactivation of the dunes seems likely

holocene stratigraphy and chronology of the casper dune field casper wyoming usa activation chronologies of dune fields within the north american great plains are significant sources of paleoclimate information although many regional chronologies exist several dune fields have been understudied including the casper dune field of central wyoming this study investigated aeolian dune sediment and buried soils of the casper dune field complex parabolic and hairpin parabolic dunes dominate the eastern dune field while simple parabolic and linear dunes dominate the western dune field buried soils are found throughout the dune field though their distribution and degree of development varies buried soils in the eastern dune field are weakly developed with typical a c profiles whereas soils in the western dune field typically exhibit a bt c profiles optically stimulated luminescence osl and radiocarbon ages were used to provide a chronology of dune field activation that spans most of the holocene at the onset of the holocene alluvium was deposited first followed by widespread d

variations in chemical composition and particle size of dune sediments along the west coast of jutland denmark abstract geochemical and textural variations in frontal dune sediments along the western coast of jutland denmark have been investigated in order to identify possible sediment provinces and transport pathways an understanding of sediment sources and sinks is important for both for an understanding of the nature of sedimentary environments and for applied coastal engineering and management purposes four coastal sectors were identified on the basis of geochemical composition one sector is compositionally different from the other three units having higher concentrations of the trace elements ni cr v sc zn pb ba zr and many rare earth elements dune sediments on this section of coast also have higher al2o3 to k2o ratios and lower al2o3 to fe2o3 ratios reflecting a lower content of feldspar and higher content of heavy minerals it is inferred that different or additional sediment source s have supplied sediment to this section of coast beach nourishment has contributed to the observed compositional differences but previous data obtained from the lodbjerg area indicate that aeolian sands on this section of coast naturally have a relatively high si fe and ti content reflecting high quartz feldspar ratio and relatively high content of heavy minerals compared with those on other sections of the coast frontal dunes along the most northern section show high abundances of k2o rb and ba reflecting a relatively high k feldspar content derived from local sources alongshore trends were also identified in the mean particle size and sorting of the frontal dunes although there is no direct correspondence with the observed geochemical differences three coastal units can be identified on the basis of particle size frontal dune sediments in the middle section are relatively coarser and less well sorted than those to the north and south probably reflecting both the addition of beach nourishment material and greater exposure to strong westerly winds which are a capable of transporting a wide range of particle sizes the three units defined on this basis do not correlate directly with the units defined on the basis of geochemical composition

fluvial transport of bovid long bones fragmented by the feeding activities of hominins and carnivores this study explores the hydraulic transportability of bovid long bone fragments created through hominin and carnivore carcass consumption in order to determine the effect of fluvial transport on the incidences of hominin and carnivore induced bone surface modifications transportability was determined using an oval race track flume and 311 long bone fragments from modern control collections of hominin and carnivore modified bone results show that the fluvial transport of long bone fragments is predicted by animal size class and bone specimen size as measured by maximum cortical thickness maximum length and maximum width all of these variables can be measured on fossil specimens long bone portion midshaft near epiphysis and epiphysis does not affect transport and hydraulic transport does not substantially modify the incidences of tooth percussion and cut marking in transported or lag assemblages in low energy fluvial environments implications of this study are 1 animal size classes and cortical thickness length and width of long bone fragments can be used to identify fluvial winnowing in fossil assemblages 2 analyses concerning the relative timing of hominin and carnivore carcass consumption based on the proportions of long bone fragments bearing tooth percussion or cut marks can be meaningfully applied to fossil assemblages deposited in low energy fluvial environments

aeolian sediment fingerprinting using a bayesian mixing model identifying sand provenance in depositional aeolian environments e g dunefields can elucidate sediment pathways and fluxes and inform potential land management strategies where windblown sand and dust is a hazard to health and infrastructure however the complexity of these pathways typically makes this a challenging proposition and uncertainties on the composition of mixed source sediments are often not reported this study demonstrates that a quantitative fingerprinting method within the bayesian markov chain monte carlo mcmc framework offers great potential for exploring the provenance and uncertainties associated with aeolian sands eight samples were taken from dunes of the small 58 km2 ashkzar erg central iran and forty nine from three distinct potential sediment sources from the surrounding area these were analyzed for 61 tracers including 53 geochemical elements trace major and rare earth elements ree and 8 ree ratios kruskal wallis h tests and stepwise discriminant function analysis dfa allowed the identification of an optimum composite fingerprint based on six tracers rb sr 87sr la yb n ga and ce and a bayesian mixing model was applied to derive the source apportionment estimates within an uncertainty framework there is substantial variation in the uncertainties in the fingerprinting results with some samples yielding clear discrimination of components and some with less clear fingerprints quaternary terraces and fans contribute the largest component to the dunes but they are also the most extensive surrounding unit clay flats and marls however contribute out of proportion to their small outcrop extent the successful application of these methods to aeolian sediment deposits demonstrates their potential for providing quantitative estimates of aeolian sediment provenances in other mixed source arid settings and may prove especially beneficial where sediment is derived from multiple sources or where other methods of provenance e g detrital zircon u pb dating are not possible due to mineralogical constraints

thermoluminescence and new 14c age estimates for late quaternary loesses in southwestern nebraska abstract loess of late quaternary age mantles most of nebraska south of the platte river valley at least five late quaternary loesses are recognized from oldest to youngest one or more undifferentiated pre illinoian loesses the loveland loess the gilman canyon loess which exhibits a well developed soil and rests unconformably on the sangamon soil the peoria loess capped by the brady soil and the bignell loess which is distributed discontinuously previous research shows that the loveland loess is illinoian the gilman canyon loess and peoria loess are wisconsin and the bignell loess is holocene we present here the first thermoluminescence tl age estimates and new 14 c ages for these late quaternary loesses at two key sections in southwestern nebraska the eustis ash pit and the bignell hill road cut tl age estimates from all samples collected from eustis ash pit and bignell hill were internally consistent tl and 14 c age estimates from these two sections generally agree and support previous age determinations the tl age estimate on loveland loess indicates deposition at 163 ka tl and radiocarbon age estimates indicate that gilman canyon loess believed to be deposited during the farmdale interstade first began to accumulate at about 40 ka the lower part of the gilman canyon loess is 36 ka at eustis and the middle of the unit is 30 ka at bignell hill the lower and upper parts of the peoria loess give age estimates of 24 ka and 17 ka respectively tl age estimates for deposition of the bignell loess are 9 ka near the base in agreement with radiocarbon age estimates and 6 ka immediately below the modern soil substantiating its holocene age comparisons of tl age estimates with 18 o and insolation curves which show loess deposition during interglacial and interstadial as well as glacial periods indicate that loess deposition on the great plains can occur under a variety of climatic conditions

interpretations and common challenges of aeolian records from north american dune fields abstract geomorphic and chronologic data for dune fields are evaluated for three contrasting areas of north america 1 the prairie parkland and boreal ecozones of the northern great plains in canada 2 the central great plains of the usa and 3 the deserts of southwestern usa and northern mexico luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply availability and mobility dune fields in the northern great plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16 11 ka subsequent aeolian deposition occurred in parkland and prairie dune fields as a result of mid holocene 8 5 ka and late holocene despite spatial and temporal gaps in chronometric data as a result of sampling biases the record from north american dune fields indicates the strong influence of sediment supply on dune construction with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre existing sediment

a middle wisconsin pollen record from hay lake arizona abstract the lower part of a 5 m core from hay lake 34 n 109 25 w at 2780 m in east central arizona provides a pollen record for the middle wisconsin identification of fossil pines is based on a key modified from hansen and cushing 1973 geological society of america bulletin 84 1181 1200 pinus edulis and p monophylla are similar in size and morphology but are significantly different from p flexilis haploxylon pines dominate the pollen record the abundance of pinyon pines during the middle wisconsin is interpreted as indicating that this group was widespread at lower elevations the local vegetation was mixed conifer forest consisting of picea p aristata p flexilis and or p strobiformis and with p ponderosa and or p contorta after about 26 000 yr b p tree line was above the elevation of hay lake the middle wisconsin climate is inferred to have been cooler than today and is marked by more available moisture that permitted pinyon pines to grow at low elevations

the origin and significance of boxwork clay coatings on dune sand grains from the nebraska sand hills usa abstract aeolian dune sands of late pleistocene to late holocene age in the nebraska sand hills are widely characterized by the development of partial clay coatings which form connected ridges and boxwork structures on the grain surfaces the proportion of sand grains with clay coatings typically shows considerable variability with depth in any given section distinct bands of sand enriched in fines are quite common especially just below the present or buried dune surfaces the morphology texture and mineralogical composition of clay coatings from two sites the merritt reservoir megabarchan and the dismal river ranch section have been investigated using a combination of sem x ray microanalysis xrd and coulter multisizer analysis in order to determine their mode of formation and environmental significance based on the analytical results and field observations it is concluded that the boxwork clay coatings formed in the vadose zone mainly as a result of precipitation and surface runoff induced infiltration of clay and very fine silt from the dune surface the main source of fines is concluded to be fine grained allochthonous aeolian dust derived principally from the high plains or more distal sources

late holocene dune accretion and episodes of persistent drought in the great plains of northeastern colorado abstract the great plains of the mid west usa contain dunefields which display stratigraphic evidence of episodic sand drift throughout the holocene and in some cases the late pleistocene widespread aeolian activity has been linked to persistent megadroughts caused by a weakening of the tropical moisture laden circulation from the gulf of mexico and equatorial pacific infrared stimulated luminescence irsl dating has been applied to two exposures in the fort morgan dunefield of northeastern colorado where radiocarbon dated buried soils provide ages for land surface stability irsl ages show that sand drift occurred episodically during the late holocene at 4 85 2 37 1 06 0 80 0 6 0 53 and 0 37 ka

climatic implications of the late quaternary alluvial record of a small drainage basin in the central great plains four late quaternary alluvial fills and terraces are recognized in wolf creek basin a small 163 km2 drainage in the kansas river system of the central great plains two terraces were created during the late pleistocene the t 4 is a fill top terrace underlain by sand and gravel fill fill i and the t 3 is a strath terrace cut on the cretaceous dakota sandstone both fill ii early holocene and fill iii late holocene are exposed beneath the t 2 a holocene fill top terrace the t 1 complex consisting of one cut and three fill top terraces is underlain by fills iii and iv a poorly developed floodplain t 0 has formed within the past 1000 yr as valleys in wolf creek basin filled during the early holocene an interval of soil formation occurred about 6800 yr b p early holocene fill has been found only in the basin s upper reaches indicating that extensive erosion during the middle holocene removed most early holocene fill from the middle and lower reaches of the basin valley filling between 5000 and 1000 yr b p was interrupted by soil formation about 1800 1500 and 1200 yr b p as much as 6 m of entrenchment has occurred in the past 1000 yr holocene events in wolf creek basin correlate well with those in other localities in the central great plains indicating that widespread changes in climate along with adjustments driven by complex response influenced fluvial activity

new geochemical evidence for the origin of north america s largest dune field the nebraska sand hills central great plains usa abstract the nebraska sand hills region is the largest dune field in north america and has diverse aeolian landforms it has been active during both the late pleistocene and late holocene despite decades of study the source of sediment for this large sand sea is still controversial here we report new trace element compositions of aeolian sand that are compared to four hypothesized sediment sources tertiary rocks of the arikaree group and ogallala group unconsolidated sands of pliocene age and platte river system sands all four potential sources have a mineralogy that is similar to the nebraska sand hills k rb k ba sc th la eu eu lan ybn as sb and fe sc values show however that pliocene sediments and sands from the platte river system are not likely sources the arikaree group could be a minor contributor but sands from the ogallala group appear to have the best compositional fit to the nebraska sand hills although past studies have proposed the ogallala group as an important sand source the hypothesis has been questioned because the unit is well cemented by calcrete in its upper part however examination of the landscape upwind of the nebraska sand hills shows that the ogallala group where it occurs at the land surface is highly dissected in much of this region which makes sand sized particles available for aeolian entrainment whenever drought conditions diminish a protective vegetation cover

fishing in a fluctuating landscape terminal pleistocene and early holocene subsistence strategies in the lake turkana basin kenya abstract during the african humid period ahp c 15 5 5 ka the rivers and lakes of much of the continent swelled due to changes in monsoonal rainfall driven by earth s orbital precession this period witnessed the growth of diverse fisher forager communities whose members adapted their settlement patterns and created new technologies in order to take advantage of aquatic resources around lake turkana in northern kenya numerous surface sites have been documented along former shorelines dating to the ahp relatively few have been excavated and dated however and just three all from the eastern basin have published faunal analyses here we present archaeofaunal assemblages from the kalokol region of the western basin where three sites with microlithic technology bone harpoons and radiocarbon dates falling within the ahp were excavated we present a detailed taphonomic assessment of the fish assemblages and a comparison with both natural and anthropogenic and ancient and modern fish bone accumulations taxa identified at the kalokol sites are discussed in terms of the occupants possible fishing technologies and strategies drawing on ethological and ethnographic data our analysis combining our data with those published from the eastern basin enables a broader discussion of how people may have responded to fluctuating ahp environments in the turkana basin

stratigraphic evidence of desertification in the west central great plains within the past 1000 yr stratigraphic and geomorphic relations archeological data and eight radiocarbon ages at five widely scattered localities in northeastern colorado indicate that eolian sand was mobilized over broad areas within the past 1000 yr the mobilization began after 1 ka was episodic and ended at some as yet undetermined time prior to the latter part of the nineteenth century given that climate model simulations suggest only slight variation in average surface temperature and annual precipitation in this region during the past 1000 yr this part of the great plains evidently is near the threshold of widespread eolian sand transport under the present climate

holocene dune activity and environmental change in the prairie parki and and boreal forest central saskatchewan canada past aeolian activity was reconstructed at four dunefields in the prairie parkland and boreal forest of central saskatchewan to elucidate landscape response to environmental change optical ages from stabilized dunes in the boreal transition ecoregion indicate two episodes of activity the first at about 11 ka corresponds to a period of early holocene parkland and grassland cover following deglaciation and drainage after about 13 0 ka and brief establishment of boreal forest the second between about 7 5 and 5 ka corresponds to a period of mid holocene parkland grassland cover optical ages from dunefields in the prairie parkland primarily record mid holocene activity between about 7 5 and 4 7 ka corresponding to a period of grassland cover with some reworking continuing into the late holocene although this area was deglaciated by about 13 5 ka there is no evidence of early holocene dune activity suggesting that mid holocene activity may have reworked earlier deposits here consequently much of the morphology and stratigraphy observed in these dunefields are associated with mid holocene activity likely associated with increased aridity and reduced vegetation cover at that time this study provides the most northerly evidence of mid holocene dune reactivation on the great plains lending support to the assertion that aeolian activity was widespread at that time

thermoluminescence ages of loess and associated sediments in central nebraska usa abstract thick deposits of quaternary loess maximum 60 m more typically 20 30 m occur in the loess hills and south of the platte river in central nebraska a programme of field sampling and thermoluminescence dating has provided new age estimates for the younger aeolian stratigraphic units in the upper part of the sequence dates from aeolian sands below the gilman canyon formation at two sites indicated ages ranging from 64 7 to 48 5 ka providing a maximum age for this unit a date of 35 3 ka was obtained from near the top of a truncated gilman canyon sequence in one section but radiocarbon evidence from other sites suggests that slow accumulation of dust accompanied by pedogenesis and syn depositional reworking continued in some areas until at least 23 ka ago the gilman canyon formation is overlain by up to 25 m of grey peoria loess which accumulated between c 22 ka and 10 5 ka ago between c 10 5 ka and 9 ka ago the rate of dust accumulation decreased apparently due to a reduction in sediment supply from the great plains river valleys thereby allowing the widespread development of a soil the brady soil after 9 ka ago the rate of dust deposition again accelerated resulting in the accumulation of up to 5 m of bignell loess the main source of bignell loess was probably also the valleys of ephemeral great plains rivers during periods when the region experienced a drier climate than present dating evidence suggests that some time after 3 2 ka ago the rate of dust accumulation again slowed allowing development of the modern soil it is suggested that this change reflected a reduction in dust availability related to a change towards slightly wetter climate and associated changes in river regime

stable isotope composition of soil organic matter and phytoliths as paleoenvironmental indicators abstract the stable c isotope composition of organic matter and opal phytoliths in diverse ecosystems demonstrate that soils carry a c isotopic signature that reflects long term inputs of above and below ground c 3 or c 4 biomass the utility of these isotopic characterization data for paleoenvironmental study is based on a knowledge of dominant soil forming processes as well as geomorphic and climatic conditions this paper reports on both the theory and applicability of isotopic characterization of soil organic c and opal phytoliths the theoretical perspectives are discussed in light of broad environmental applications details of the sample collection and preparation are provided with insights into quantities and pretreatment required for stable c isotopic characterization two case studies from the central great plains region are presented paleoclimatic interpretations are discussed for a portion of the central great plains these interpretations are based on the stable c isotope data recovered from holocene paleosols these data indicate higher proportions of c 3 vegetation persisted during the early holocene the concordance in the c isotopic signatures of soil organic matter and phytoliths provide strong biological evidence of regionally cooler conditions this c isotopic concordance also appears during the mid holocene c isotope values indicate an increase in the proportion of c 4 vegetation which reflects regionally warmer climatic conditions than present isotopic discordance in soil organic c and phytoliths can indicate the degree of diagenesis resulting from pedological alteration geomorphic and pedologic evidence indicate that the c isotope discordance between soil organic matter and opal phytoliths is the result of local topographic variations and spatial heterogeneity associated with plant distribution

textural geochemical and mineralogical evidence for the sources of aeolian sand in central and southwestern nebraska u s a abstract stabilised quaternary dunefields in the central united states underwent multiple episodes of dune activity in the holocene and may undergo extensive reactivation in response to future changes in global climate however the sources of aeolian sand and the history of sand supply in these dunefields are poorly understood an investigation was therefore undertaken to identify the source s of aeolian sand in the largest dunefield on the high plains the nebraska sand hills and an adjacent area of dunes referred to here as the dickens dunefield the specific hypotheses relating to sand provenance were 1 that the nebraska sand hills dune sands were derived from the underlying fluvial sands 2 the dickens dune sands were derived from migrating nebraska sand hills dunes and 3 the dickens dune sands were derived from south platte river sand statistical comparison of the textural and compositional characteristics of the aeolian and possible source sands suggested that the nebraska sand hills were indeed derived from the underlying fluvial sediments following an extensive episode of fluvial reworking which occurred at some time between the late pleistocene and middle holocene the dickens dune sands were probably derived from the south platte river at some time during the holocene

late quaternary stratigraphy and geochronology of the western killpecker dunes wyoming usa abstract new stratigraphic and geochronologic data from the killpecker dunes in southwestern wyoming facilitate a more precise understanding of the dune field s history prior investigations suggested that evidence for late pleistocene eolian activity in the dune field was lacking however luminescence ages from eolian sand of 15 000 yr as well as folsom 12 950 11 950 cal yr b p and agate basin 12 600 10 700 cal yr artifacts overlying eolian sand indicate the dune field existed at least during the latest pleistocene with initial eolian sedimentation probably occurring under a dry periglacial climate the period between 13 000 and 8900 cal yr b p was characterized by relatively slow eolian sedimentation concomitant with soil formation erosion occurred between 8182 and 6600 cal yr b p on the upwind region of the dune field followed by relative stability and soil formation between 5900 and 2700 cal yr b p the first of at least two latest holocene episodes of eolian sedimentation occurred between 2000 and 1500 yr followed by a brief 500 yr episode of soil formation a second episode of sedimentation occurring by at least 700 yr may coincide with a hypothesized medieval warm period recent stabilization of the western killpecker dunes likely occurred during the little ice age 350 100 yr b p the eolian chronology of the western killpecker dunes correlates reasonably well with those of other major dune fields in the wyoming basin suggesting that dune field reactivation resulted primarily due to departures toward aridity during the late quaternary similar to dune fields on the central great plains dune fields in the wyoming basin have been active under a periglacial climate during the late pleistocene as well as under near modern conditions during the latest holocene

sheltered sandy beaches of southwestern australia four beach types were identified from field surveys of beach profiles on low energy sandy beaches in cockburn sound a micro tidal semi enclosed basin in southwestern australia these were delineated by an exposure factor ef which provided a surrogate for the relationship between incident wave energy and attenuation as a result of structures banks and shoals the four beach profiles identified were exponential segmented concave curvilinear and convex curvilinear in form whether the different profile shapes occurred in environments subject to different degrees of sheltering and protection under the same tidal regime was open to question beach profiles were examined for como beach and princess royal harbour in western australia and compared with observations from cockburn sound to test this proposition cockburn sound and princess royal harbour are subject to minimal penetration of swell waves whereas como beach in the swan river estuary is wholly fetch limited profile forms identified in each environment were consistent with those described from cockburn sound similar profile types had similar exposure values for all sites such that ef 2 of convex curvilinear although this approach requires further testing in low energy environments subject to different tidal ranges and fluctuations in sea level use of the exposure factor for delineation of low energy sheltered beach types appears to be a robust procedure

the blackwater draw formation quaternary a 1 4 plus m y record of eolian sedimentation and soil formation on the southern high plains the southern high plains of northwestern texas and eastern new mexico are mantled by a vast 100 000 km 2 sheet of quaternary eolian sediment locally as much as 27 m thick and termed the blackwater draw formation these sediments generally fine from southwest to northeast exhibiting a linear relationship of decreasing sand content and sand size and increasing silt content with increasing distance indicating the source area to be the pecos river valley as many as six well developed buried soils 2 5yr to 5yr hues bt horizons 1 2 m thick stage ii iii calcic horizons similar to the regional paleustalf and paleustoll surface soils occur in the formation the buried soils indicate episodic sedimentation separated by long periods of landscape stability eolian sedimentation probably occurred during prolonged aridity and stability and pedogenesis likely obtained during subhumid to semiarid conditions similar to those of the late quaternary the presence of the 0 62 m y lava creek b ash and the 1 4 m y guaje ash in the formation shows that the deposit accumulated throughout most of the quaternary data from paleomagnetic thermoluminescence and radiocarbon studies suggest that each cycle of sedimentation stability lasted for several hundred thousand years and that the last depositional event occurred at least several tens of thousands of years ago

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

late pleistocene marine birds from southern peru distinguishing human capture from el nino induced windfall abstract the central andean hyperarid littoral has abundant marine fauna that would have been attractive to the earliest inhabitants whether people hunted or scavenged marine animals during the terminal late pleistocene have social and technological implications for understanding ancient andean foraging the periodic phenomenon of el nino southern oscillation enso disrupts marine food chains and results in the death of significant numbers of marine vertebrates and microorganisms the onset of ancient el nino events may have created a subsistence opportunity for human coastal inhabitants along the pacific coast of the central andes when large numbers of guano producing birds cormorants boobies and pelicans became weak and eventually died the remains of numerous marine birds dominate the late pleistocene archaeological site of quebrada tacahuay in far southern peru this terminal pleistocene occupation dating to 10 770 10 290 years ago uncalibrated radiocarbon years 12 880 11 970 calendar years ago was buried and sealed by an apparent ancient el nino induced debris flow using characteristics of the faunal assemblage i assess whether people hunted marine birds or enso created a subsistence opportunity for people to either scavenge a catastrophic assemblage or collect a community of vulnerable birds prior to the debris flow i present avian skeletal part frequencies butchering patterns and the quantities and variety of marine bony fishes an analysis of vertebrate taxonomic and skeletal composition in conjunction with an analysis of site context does not support the hypothesis that paleoenvironmental conditions generated an opportunity for the facile collection of either dead or weak birds in contrast the faunal data suggest that humans actively hunted captured and consumed healthy marine birds when evaluating the possible role of environmental fluctuations on human behavior and diet researchers must consider not only the taphonomy of the most abundant remains but also how other vertebrate taxa in a region are affected as well as the archaeological context

late pleistocene dune activity in the central great plains usa abstract stabilized dunes of the central great plains especially the megabarchans and large barchanoid ridges of the nebraska sand hills provide dramatic evidence of late quaternary environmental change episodic holocene dune activity in this region is now well documented but late pleistocene dune mobility has remained poorly documented despite early interpretations of the sand hills dunes as pleistocene relicts new optically stimulated luminescence osl ages from drill cores and outcrops provide evidence of late pleistocene dune activity at sites distributed across the central great plains in addition late pleistocene eolian sands deposited at 20 25 ka are interbedded with loess south of the sand hills several of the large dunes sampled in the sand hills clearly contain a substantial core of late pleistocene sand thus they had developed by the late pleistocene and were fully mobile at that time although substantial sand deposition and extensive longitudinal dune construction occurred during the holocene many of the late pleistocene osl ages fall between 17 and 14 ka but it is likely that these ages represent only the later part of a longer period of dune construction and migration at several sites significant late pleistocene or holocene large dune migration also probably occurred after the time represented by the pleistocene osl ages sedimentary structures in late pleistocene eolian sand and the forms of large dunes potentially constructed in the late pleistocene both indicate sand transport dominated by northerly to westerly winds consistent with late pleistocene loess transport directions numerical modeling of the climate of the last glacial maximum has often yielded mean monthly surface winds southwest of the laurentide ice sheet that are consistent with this geologic evidence despite strengthened anticyclonic circulation over the ice sheet mobility of large dunes during the late pleistocene on the central great plains may have been the result of cold short growing seasons with relatively low precipitation and low atmospheric co 2 that increased plant moisture stress limiting the ability of vegetation to stabilize active dune sand the apparent coexistence of large mobile dunes with boreal forest taxa suggests a late pleistocene environment with few modern analogs

formation of quartz silt during humid tropical weathering of dune sands abstract quartz dune sand grains in northeast australia break down in situ under humid tropical weathering conditions to form substantial amounts of silt fragmentation appears to occur primarily due to silica solution along microfractures and dislocation structures in grains which have experienced tectonic deformation prior to deposition the surface textures of quartz grains viewed with the sem exhibit a close dependency on crystallographic properties in the b and c horizons of some weathered late pleistocene dunes silt forms up to 10 of the bulk sediment local remobilisation of such deposits by wind allows selective removal of the silt which is later deposited as a thin surficial sheet in more sheltered areas downwind these observations provide further evidence that weathering processes provide a major mechanism of silt formation and are an important factor to be considered in relation to the origin of loess and siltstones

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

late holocene alluvial chronology and climate change in the central great plains abstract alluvium in one reach of the republican river valley south central nebraska dates to the holocene radiocarbon dating of fills underlying the two terraces in the valley reveals that entrenchment between 4500 and 3700 yr b p formed the high terrace subsequently alternating aggradation and stability occurred until sometime between 1800 and 1100 yr b p following another period of alluviation channel incision formed the low terrace general synchrony between this chronology and other late holocene fluvial chronologies of the central great plains suggests climatic control of fluvial activity the episodes of incision are tentatively correlated with different climate regimes illustrating the difficulty of attributing a given fluvial response to a particular direction of climatic change

patterns of holocene environmental change in the midwestern united states abstract four pollen sequences along a transect from north central iowa to southeast wisconsin reveal the distribution of prairie and forest during the holocene and test the use of pollen isopolls in locating the holocene prairie forest border prairie was dominant in central iowa and climate was drier than present from about 8000 to 3000 yr b p during the driest part of this period in central iowa 6500 5500 yr b p mesic forest prevailed in eastern iowa and wisconsin suggesting conditions wetter than at present prairie replaced the mesic forest about 5400 yr b p in eastern iowa but did not extend much farther east mesic forests were replaced in southern wisconsin and northern illinois about 5400 yr b p by xeric oak forests this change from mesic to xeric conditions at 5400 yr b p was widespread and suggests that the intrusion of drier pacific air was blocked by maritime tropical air from the gulf of mexico until the late holocene in this area

origin of the late quaternary dune fields of northeastern colorado stabilized eolian deposits mostly parabolic dunes and sand sheets cover much of the landscape of northeastern colorado and adjacent parts of southwestern nebraska in four geographically distinct dune fields stratigraphic and soil geomorphic relations and accelerator radiocarbon dating indicate that at least three episodes of eolian sand movement occurred between 27 ka and 11 ka possibly between 11 ka and 4 ka and within the past 1 5 ka thus eolian sand deposition took place under both glacial and interglacial climatic conditions in the youngest episodes of eolian sand movement holocene parabolic dunes partially buried pleistocene sand sheet deposits late holocene sands in the fort morgan and wray dune fields to the south of the south platte river have trace element ratios that are indistinguishable from modern south platte river sands but different from ogallala formation bedrock which has previously been cited as the main source of dune sand on the great plains sands in the greeley dune field to the north of the south platte river have trace element concentrations that indicate a probable laramie formation source measurements of parabolic dunes indicate paleowinds from the northwest in all dune fields in good agreement with resultant drift directions calculated for nearby weather stations thus paleowinds were probably not significantly different from present day winds and are consistent with a south platte river source for the fort morgan and wray dune fields and a laramie formation source for the greeley dune field sand accumulated downwind of the south platte river to form the fort morgan duen field in addition sand was also transported farther downwind over the upland formed by the calcrete caprock of the ogallala formation and deposited in the lee of the upland on the southeast side because of high wind energy the upland itself served as a zone of sand transport but little or no sand accumulation took place on this surface these studies which demonstrate the importance of fluvial source sediments for dune fields in colorado may be applicable to other dune fields in north america because modern drift potentials in northeastern colorado are among the highest in the world the present stability of dunes in the region may be in part a function of the dunes being supply limited rather than solely transport limited extensive 7700 km2 late holocene dunes document that eolian sand in northeastern colorado is very sensitive to small changes in climate or fluvial source conditions

stoss side mud drapes deposits of interdune pond margins arcuate mud drapes have been observed in an interdune area in southern tunisia they are believed to have been formed by deposition from ponded water around aeolian dunes during flood events they are preferentially preserved on the stoss side of the dunes as a result of subsequent dune migration and exhibit extensive evidence of animal tracks they are useful in illustrating dune interdune dynamics and recording the type of animals present

twentieth century dune migration at the great sand dunes national park and preserve colorado relation to drought variability abstract the great sand dunes national park and preserve in southern colorado contains a large dune mass banked against the sangre de cristo mountains the dune mass is bounded for hundreds of kilometers by a vegetated low relief sand sheet with abundant active parabolic and barchanoid dunes the clear morphology of these dunes formed by winds mostly from the southwest and the unambiguous identification of these forms in remotely sensed images provide straightforward targets to assess temporal changes in dune position a digital database of georeferenced remote sensing images from 1936 to 1999 is used to quantify parabolic and barchan dune migration rates and surface reflectance an indicator of vegetation cover with evolving drought conditions in the twentieth century the total net migration of 13 parabolic dunes in 63 years is 0 31 to 0 66 km whereas 11 barchan dunes moved an average of 0 12 to 0 47 km compared to intervening wet year there is at least a three fold increase in average parabolic dune migration during well documented droughts in the 1930s 1950s and 1990s with a concomitant reduction in vegetation cover and surface water resources the landscape response to the most recent drought in the late twentieth century is documented by an average parabolic dune migration rate of 30 m year which is a six fold acceleration over prior wet years and similar to dune response during the 1930s a nonlinear threshold for parabolic dune migration is indicated with lower quartile palmer drought severity index values of

origin of late quaternary dune fields on the southern high plains of texas and new mexico mostly stabilized late holocene eolian sands on the southern high plains of the united states were studied to determine their origins and to assess whether present dune stability depends more strongly on sediment supply sediment availability or transport limitations geomorphic sedimentological and geochemical trends indicate that late holocene dunes formed under westerly paleowinds broadly similar to those of today mineralogical and geochemical data indicate that the most likely source for the sands is not the pecos river valley but the pleistocene blackwater draw formation an older extensive eolian deposit in the region these observations suggest that new sand is supplied whenever vegetation cover is diminished to the extent that the blackwater draw formation can be eroded in agreement with modern observations of wind erosion in the region we conclude therefore that southern high plains dunes are stabilized primarily due to a vegetation cover the dunes are thus sediment availability limited this conclusion is consistent with the observation that in the warmest driest part of the region where vegetation cover is minimal dunes are currently active over a large area geochemical data indicate that southern high plains dunes are the most mineralogically mature quartz rich sands yet studied in the great plains which suggests a long history of eolian activity either in the dune fields or during deposition of the blackwater draw formation