origin and evolution of lunettes on the high plains of texas and new mexico lunettes isolated dunes on the lee side of playa basins are common landforms on the southern high plains of northwest texas and eastern new mexico the dunes contain calcareous 15 40 caco3 sandy loam or loamy sand with minor amounts of sepiolite deposited 25 000 800014c yr b p and derived by deflation of lacustrine carbonate in the basins the dunes also contain low carbonate 0 15 caco3 sand or loamy sand that was deposited 25 000 15 000 yr b p and 8000 5000 yr b p and was derived by deflation that created the basins or deflated from sand deposited in the basins buried soils are common in the lunettes a bk profiles characterize soils formed in the calcareous sandy loam the sandy low carbonate sediments contain a bt profiles in the oldest sand of some dunes and a bw a bt or a btk in the early and middle holocene sand the dune stratigraphy combined with carbon isotope data derived from dated a horizons in lunettes suggests the following scenario for the southern high plains the lunettes began forming as low carbonate sand dunes in the late pleistocene as playa basins were formed or deepened by wind erosion the erosion repeatedly alternated with stability the environment probably was cool and dry but one or more cool and wet intervals 25 000 15 000 yr b p resulted in a rise in the water table and deposition of lacustrine carbonate in the deepest basins there may have been short departures toward warmer and probably toward drier conditions throughout this time episodically dry conditions 15 000 8 000 yr b p resulted in deflation of the carbonate and further dune construction by repeated accretion of calcareous sandy loam or loamy sand the low carbonate sand was deposited during widespread drought and deflation 8000 5000 yr b p the dunes have been largely stable in the late holocene

testing optically stimulated luminescence dating of sand sized quartz and feldspar from fluvial deposits abstract we apply single aliquot optically stimulated luminescence osl dating to quartz and feldspar rich extracts from fluvial channel deposits of the rhine meuse system in the netherlands the time of deposition of these deposits is tightly constrained by radiocarbon dating or historical sources this allows us to compare osl ages obtained on quartz and infrared osl ir osl ages obtained on potassium rich feldspar with independent ages over the range of 0 3 13 ka we show that the quartz osl ages are in good agreement with the expected age using ir osl dating of feldspar we find a slight age overestimate for the youngest sample whereas for older samples the age is significantly underestimated we also apply osl dating to older fluvial and estuarine channel deposits with limited independent chronological constraints comparison of feldspar ir osl ages with the quartz osl ages up to 200 ka shows a clear trend where the former severely underestimates the latter this trend is similar to that found for the samples with independent age control indicating that the feldspar ir osl ages are erroneously young for the entire age range in the youngest samples incomplete resetting of the ir osl signal prior to deposition probably masks the age underestimation we show that the ir osl age underestimation is partly caused by changes in trapping probability due to preheating correction for this phenomenon improves the ir osl ages slightly but does not provide a complete solution to the discrepancy we suggest that in the light of the problems encountered in the ir osl dating of feldspar quartz is the mineral of choice for osl dating of these deposits however feldspar dating should continue to be investigated because it has potential application to longer time scales

new data on the stratigraphy and pedology of the clovis and plainview sites southern high plains abstract the well known clovis and plainview archaeological sites of new mexico and texas have yielded new data on regional late quaternary geologic paleoclimatic and pedologic histories eolian sedimentation at the clovis site from about 10 000 to less than 8500 yr b p was followed by the formation of a cumulic soil between 8500 and 5000 yr b p episodic eolian and slope wash deposition then culminated in massive eolian sedimentation about 5000 yr b p after which a haplustalf formed then was subsequently buried by part of a dune system within the last 1000 yr at the plainview site a basal stream gravel contains plainview cultural material ca 10 000 yr b p which is followed by a localized early holocene lacustrine deposit two eolian deposits the younger dating to about 5000 yr b p and a marsh deposit which slowly accreted as an argiustoll formed in the younger eolian unit the data indicate that on the southern high plains 1 between 12 000 and 8500 yr b p sedimentation varied from site to site 2 there was a regional climate change toward warming and drying in the early holocene 3 two episodes of severe drought apparently occurred in the middle holocene 6500 to 4500 yr b p 4 between 4500 yr b p and the present an essentially modern climate existed but with several shifts toward aridity within the last 1000 yr 5 argillic horizons have developed in late holocene soils 6 clay illuviation can occur in calcareous soils and 7 long distance correlation of holocene stratigraphy in the region is possible particularly with the aid of soil morphology

geologically constrained morphological variability and boundary effects on embayed beaches abstract headlands rock outcrops and engineering structures impact beach and nearshore dynamics of coastal embayments inducing boundary effects that constrain the lateral and vertical beach variability this study analyses morphological change in six embayed beaches with diverse levels of exposure to wave action and various degrees of geological control in the mesotidal coast of southwestern portugal the aim is to identify whether geological boundaries constrain the morphological behaviour of embayed beaches and assess whether their effects can be decoupled from datasets of morphological change topographic data obtained over a two year period on each of the six embayments were analysed using empirical orthogonal functions eof to decompose temporal and spatial variability in the datasets first and second mode eigenfunctions were explored using time variable linear correlation analysis with several nearshore parameters that include hydrodynamic variables sedimentary and geometric characteristics of each embayment in order to derive forcing response relationships our results demonstrate that natural geological boundaries constrain the morphological behaviour of embayed beaches producing conspicuous alongshore variability in all embayments localised responses induced by lateral and vertical boundary interference with beach and nearshore dynamics include beach rotation topographically controlled rip circulation and restrained profile fluctuation spatial decoupling in cross and longshore responses is accompanied by a temporal decoupling in response times both of which are slower in more constrained embayments from 1 day in exposed embayments to 1 week or more in the most sheltered ones normalised wave power was correlated at the 99 confidence level with the primary mode of morphological variability at most embayments which represent 67 to 94 of the variance in the datasets this correlation stresses the importance of combined parameterization of wave and tide forcing in process response relations between hydrodynamics and morphological change for mesotidal coastal environments lateral and vertical geological boundaries exert their effects fundamentally by restraining longshore sediment transport inducing cellular surf zone circulation and by impacting cross shore sediment transport it is postulated that decreasing sediment abundance and substrate depth intensify vertical boundary effects while higher indentation and wave obliquity enhance the effects of lateral boundaries

late holocene eolian activity in the mineralogically mature nebraska sand hills abstract the age of sand dunes in the nebraska sand hills has been controversial with some investigators suggesting a full glacial age and others suggesting that they were last active in the late holocene new accelerator mass spectrometry radiocarbon ages of unaltered bison bones and organic rich sediments suggest that eolian sand deposition occurred at least twice in the past 300014c yr b p in three widely separated localities and as many as three times in the past 80014c yr at three other localities these late holocene episodes of eolian activity are probably the result of droughts more intense than the 1930s dust bowl period based on independent great plains climate records from lake sediments and tree rings however new geochemical data indicate that the nebraska sand hills are mineralogically mature eolian sands in nebraska have lower k feldspar and k2o rb and ba contents than most possible source sediments and lower k feldspar contents than dunes of similar age in colorado the most likely explanation for mineralogical maturity is reduction of sand sized k feldspar to silt sized particles via ballistic impacts due to strong winds over many cycles of eolian activity therefore dunes of the nebraska sand hills must have had a long history probably extending over more than one glacial interglacial cycle and the potential for reactivation is high with or without a future greenhouse warming

late quaternary hillslope evolution recorded in eastern south african colluvial badlands abstract infrared stimulated luminescence irsl ages have been obtained from a sequence of sandy colluvial deposits in northern kwazulu natal comparison of the irsl ages on sand sized potassium rich feldspars with radiocarbon dates on a horizon organic matter from buried palaeosols within the colluvial succession shows good agreement between the dating techniques when compared with palaeoenvironmental records the data suggest that the colluvium accumulated during arid stages of the late quaternary whilst pedogenesis repeatedly occurred at intervals of hillslope stability which may reflect periods of greater humidity temperature does not seem to have been a forcing factor in the landscape development extensive colluviation took place during the arid last glacial maximum but the occurrence of several palaeosols indicates that it was a time of fluctuating climatic conditions

luminescence chronology of late pleistocene glacial deposits in north westland new zealand abstract the chronology of the late pleistocene glacial history of north westland south island of new zealand is refined by luminescence dating of sediments it is demonstrated by two case studies that ages determined by different luminescence techniques agree well with the results of radiocarbon dating luminescence ages determined for sediments from two key sites of the loopline formation confirm the previous correlation of this unit with marine isotope stage mis 4 this indicates that late pleistocene glaciers reached their last maximum extent in north westland during the early part of the otira last glaciation furthermore initial dating evidence on coarse alluvial deposits in the lowlands indicates their formation during mis 5b and mis 5d it is probable that these coarse gravel deposits are outwash related to glacial advances if so both advances were probably much less extensive than the glaciations during mis 4 and mis 2

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

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

eolian landscape evolution and soil formation in the chaco dune field southern colorado plateau new mexico abstract eolian deposits of the chaco dune field cover a broad expanse of the southeastern colorado plateau in new mexico and comprise a large part of the late quaternary sedimentary record in this region the primary eolian landforms include sand sheets parabolic and modified parabolic dunes barchan barchanoid dune complexes and ridge dunes many of the eolian landforms in the chaco dune field have remained stable over a sufficiently long time to permit soil development weakly to moderately developed calcic soils which formed in eolian deposits of mid holocene and latest pleistocene age possess clay enriched weak argillic b horizons these soils have been buried progressively by younger eolian sediments forming regionally correlative bounding surfaces over the chaco dune field and recording relict latest pleistocene and middle holocene eolian landscapes soil geomorphic relations and radiocarbon dated material within the eolian deposits have been useful in 1 delineating three regionally correlative soil stratigraphic units and their associated landforms and 2 studying the types and rates of landscape evolution and climatic changes within this portion of the colorado plateau the most significant period of eolian landform construction is inferred to have occurred during the latest pleistocene glacial to interglacial climatic change forming widespread sand sheets and modified parabolic dunes eolian deposition during the middle and late holocene were dramatically influenced by the presence of previously developed latest pleistocene to early holocene buried soils which may have enhanced sand sheet and parabolic dune development due to the binding effect of the soils middle holocene eolian deposition may be related primarily to neoglacial climatic changes which enhanced ground surface moisture and promoted sand sheet and parabolic dune formation the youngest period of wolian deposition occurred after 1 5 ka and resulted in the formation of the most diverse suite of eolian landforms and deposition of volumetrically more eolian sediments than the mid holocene event in contrast to earlier interpretations the classic mid holocene or altithermal event apparently did not play a major role in the formation of eolian landscapes in the chaco dune field

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

evidence of holocene aeolian activity in sand dunes from lapland abstract infra red stimulated luminescence irsl dating has been applied to potassium rich feldspars separated from aeolian sands from seven sites in lapland a single aliquot additive dose procedure has been used to show that the sands were well bleached at deposition despite the high latitudes of the sampling sites the irsl dates have been compared with independent age control in the form of radiocarbon dates on charcoal from within the same sections and all show good agreement independently controlled irsl ages as young as 500 years show that this method can be accurately applied to geologically recent sediments the primary phase of dune stabilisation across lapland has been shown to have occurred later than was previously thought during the mid holocene the most recent deflation episode occurred during the last 800 years within the little ice age and thus may be a climatically controlled event

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

infra red stimulated luminescence ages from aeolian sand and alluvial fan deposits from the eastern mojave desert california abstract infra red stimulated luminescence irsl from coarse grained 180 212 m potassium rich feldspars has been used to date deposits associated with the western piedmont of the providence mountains in the eastern mojave desert these deposits consist of alluvial fans aeolian sand which exists in the form of lenses within the fan matrices and sand from the kelso dune field which abuts the distal end of the fan sequence deposition and subsequent stabilisation of these sand units appears to have occurred in both aird and intermittent climates associated with pluvial phases during the holocene and late pleistocene ages of 6600 870 and 7840 1790 years were obtained from dune sand bracketing the mazama ash at skull creek dunes oregon giving an independent age control on the single aliquot irsl method which was used on the mojave samples

holocene development of multiple dune generations in the northeast rub al khali united arab emirates it has been hypothesised that in sand seas where multiple dune generations occur each generation represents a distinct terrestrial response to contrasting palaeoatmospheric circulation conditions lancaster n kocurek g singhvi a pandey v deynoux m ghienne j f et al 2002 late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania geology 30 991 994 however reconstructing dunefield accumulation and preservation chronologies has often utilised a limited suite of samples because of the difficulties realised in accessing unconsolidated aeolian sands which has limited the capacity to test this hypothesis in the eastern united arab emirates artificial excavation for quarrying and construction have generated a unique opportunity to examine and sample the internal structures of dune systems and to generate data to test the hypothesis of dune generational development this paper presents new data and chronologies from a multigenerational analysis of dune

middle holocene drought on the southern high plains abstract the climate of the southern high plains during the middle holocene is indicated by data from a variety of sources stratigraphic geomorphic and pedologic research at six localities in draws several dune sites and one playa lake basin show that widespread eolian erosion and sedimentation began in some areas by 9000 yr b p and culminated 6000 4500 yr b p probably because of warmer drier conditions that reduced the vegetative cover archaeological investigations at three sites provide evidence for the excavation of wells at this time apparently because of a declining water table studies of a few vertebrate and invertebrate faunas also indicate warming and drying in the middle holocene climate models and very limited isotopic data from bison bone suggest that summers in the middle holocene were warmer than present with reduced effective precipitation all lines of evidence indicate that the southern high plains was subjected to prolonged drought in the middle holocene with a maximum between 6500 and 4500 yr b p conforming climatically and chronologically to the altithermal

stability of holocene climate regimes in the yellowstone region abstract a 12 500 yr pollen record from loon lake wyoming provides information on the climate history of the southwestern margin of yellowstone national park the environmental reconstruction was used to evaluate hypotheses that address spatial variations in the holocene climate of mountainous regions loon lake lies within the summer dry winter wet climate regime an increase in xerophytic pollen taxa suggests drier than present conditions between ca 9500 and 5500 14 c yr b p this response is consistent with the hypothesis that increased summer radiation and the expansion of the east pacific subtropical high pressure system in the early holocene intensified summer drought at locations within the summer dry winter wet regime this climate history contrasts with that of nearby sites in the summer wet winter dry region which were under the influence of stronger summer monsoonal circulation in the early holocene the loon lake record implies that the location of contrasting climate regimes did not change in the yellowstone region during the holocene the amplitude of the regimes however was determined by the intensity of circulation features and these varied with temporal changes in the seasonal distribution of solar radiation

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

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

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

middle and late holocene dune reactivation in the nebraska sand hills usa a combination of optical dating of aeolian sand and radiocarbon dating of palaeosols and interdune sediments has allowed some refinements to the chronostratigraphy of the nebraska sand hills our results directly confirm previous inferences that multiple phases of aeolian deposition including megabarchan dune reactivation occurred within the sand hills during the middle and late holocene optical dates on stratified aeolian barchan dune sediments from two localities provide ages ranging from c 6 ka to 300 years ago weakly developed palaeosols intercalated within the dune sediments and other forms of post depositional modification indicate periods of relative stability and reduced dune mobilization optical dates on the upper 12 15 m of two dune exposures indicate repeated possibly regionally correlative reactivations which occurred between c 400 500 and 200 300 years ago comparison of late holocene aeolian activity with local and regional palaeoclimatic proxy records suggests that dune reacti

groundwater hydrochemistry and soil pollution in a catchment affected by an abandoned lead zinc mine functioning of a diffuse pollution source the importance of polluted alluvial soils as a potential diffuse source of heavy metals was investigated in a catchment of the matylda stream affected by an abandoned lead and zinc ore mine in upper silesia southern poland this was attempted by means of standard groundwater analyses performed together with measurements of cd pb zn fe and mn concentrations in soil and groundwater the matylda stream receiving mine water was converted in the 20th century into a straight channel directed in its middle reach over the valley bottom this changed the drainage direction of the matylda stream water during mining operations groundwater seepage combined with surface drainage by shallow ditches caused pollution of sandy soils exceeding over 100 mg kg of cd 24 of zn and 4 of pb at surface or subsurface soil horizons and reaching at least 60 cm in depth after mine closure in the 1970s the network of ditches appears to be a source of ca mg chlorides carbonates and nitrates as indicated by the more or less regular increase of these major ion concentrations in groundwater down ditches whereas the ditches are a sink rather than a source of zinc cadmium and lead in permanently dry reaches or transition zones in reaches with surface water flowing periodically the metal concentrations and distribution in soil and groundwater suggest the slow mobilization of heavy metals stored in the valley bottom and the minor importance of soil as a diffuse source for surface water pollution

spatial variations of holocene climatic change in the yellowstone region abstract the paleoecologic record of the northern rocky mountains shows considerable spatial variability which has been difficult to explain as a unified response to large scale changes in effective moisture or temperature through time comparison of past and present climatic patterns suggests that the spatial heterogeneity in the fossil record arises from a local response to the effects of greater summer solar radiation during the early holocene solar radiation directly determines evapotranspiration and indirectly controls the strength of the summer monsoon and the eastern pacific subtropical high pressure system the yellowstone region provides an example of an area where the indirect effects of solar radiation are manifest by the juxtaposition of two contrasting climatic regimes today and where these regimes were amplified during the early holocene fossil pollen data suggest that central and southern yellowstone the summer dry area became drier in the early holocene while northern yellowstone the summer wet area became wetter the boundary between regimes however is controlled by topography and has not changed significantly in the holocene the spatial variations of holocene vegetation and climatic changes in the northern rocky mountains may therefore be explained as a trade off between strengthened monsoonal circulation and a stronger subtropical high in the early holocene and the relative importance of these precipitation regimes on a topographically complex landscape

hydrologic variation in the northern great plains during the last two millennia abstract reconstructions of lake water salinity at decadal resolution for the last 2000 yr are compared among three lakes in north dakota to infer regional patterns of drought the intersite comparisons are used to distinguish local variation in climate or hydrology from regional patterns of change at one lake diatom inferred salinity and lake water mg ca inferred from ostracode shell chemistry are coherent both in terms of direction and magnitude of change indicating that each is a robust technique for reconstructing lake water chemistry the data show that the last 2000 yr have been characterized by frequent shifts between high and low salinity suggesting shifts between dry and moist periods long intervals of high salinity suggest periods of multiple decades when droughts were intense and frequent thus indicating times when drought was more persistent than in the 20th century both the medieval period and little ice age were hydrologically complex and there is no clear evidence to suggest that either interval was coherent or unusual in effective moisture relative to long term patterns differences among the three sites may be attributed to variation in local hydrology and these differences emphasize the need for multiple sites in deriving regional climate interpretations from paleoecological data

ground water processes controlling a prairie lake s response to middle holocene drought lake response to climate forcing is commonly regarded as being controlled by within lake processes we present a case from the northern great plains in which holocene drought response recorded in lake sediments was determined by changes in chemical characteristics of source ground water middle holocene ostracode assemblages were dominated by halophylic limnocythere staplini indicating increased lake water salinity yet the oxygen isotope values in this period decreased by 2 to 3 contrary to expectations of evaporative dominance we infer from these proxy records and ground water flow model results that the paleoclimatic record in the lake was mediated by changes in ground water catchment area and by reduction in evapotranspiration accompanying desiccation of peripheral lake basins

a solution to anomalous fading and age shortfalls in optical dating of feldspar minerals abstract recent reports of age underestimations for events of interest in both palaeoclimatology and archaeology have led to questioning the validity of using luminescence for dating sediments the commonly designated culprit is anomalous fading of feldspar luminescence we investigated the differential fading rates of single feldspar grains in sediment samples from different geological domains of north america and deduced how one could extrapolate to zero fading this is shown to resolve an extreme case of optical age underestimation documented for the late pleistocene norfolk formation a key palaeoclimate stratigraphic unit exposed along the north american atlantic coast

sediment magnetic signature of climate in modern loessic soils from the great plains our magnetic analysis of 40 modern loessic soil profiles from the midwestern united states shows that the upper soil horizons of all sites are characterized by an increase in the concentration of fine grained do0 1mm ferrimagnetic minerals magnetite and or maghemite our sites were selected from stable upland positions along a precipitation gradient extending from sw nebraska mean ann precip o500 mm yr to central missouri mean ann precip 41000 mm yr changes in magnetic remanence parameters irm arm and magnetic susceptibility w between soil and parent material vary systematically along the transect and are likely to reflect changes in source area and transport distance magnetic enhancement is calculated for several magnetic parameters by taking the ratio menhanced mparent material where m stands for either arm irm or w our analyses show that magnetic enhancement of modern soils based on irm and w correlates with changes in mean annual precipitation the best correlation however is observed when arm is used as a proxy of magnetic enhancement which might reflect the bias of arm towards small single domain grains of likely pedogenic origin our study shows that magnetic soil properties in combination with non magnetic proxies such as solum depth b horizon color depth to carbonates or other weathering indices have the potential to yield reliable reconstructions of paleoclimate in parts of the great plains where well preserved loessic paleosols exist

effects of storminess sand supply and the north atlantic oscillation on sand invasion and coastal dune accretion in western portugal holocene forested coastal dunes fringe the atlantic coast of western portugal mapping of dunes in the field and using air photographs shows a range of forms reflecting dominant northwest and westerly onshore wind regimes planting of maritime pine forests in the thirteenth and twentieth centuries was initiated because of sand invasion causing problems for human settlement and agriculture early holocene dunes have a well developed podsol and date to 9 7 and 8 2 ka suggesting at least some of these sands may have been emplaced during a global cooling event significant transgressive dune accretion at 2 2 and 1 5 ka implies abundant sand supply and strong onshore winds the most recent dune building period dates to ad 1770 1905 and coincides with a predominantly negative winter north atlantic oscillation index naoi accretion of dunes along the portuguese coast appears out of phase with dune development in southwest france which may reflect different atlantic storm tracks driven by changes in the domin

optical dating of holocene dune sands in the ferris dune field wyoming abstract optical dating of late quaternary quartz dune sands from the clear creek portion of ferris dune field wyoming demonstrates the considerable potential of the technique as a chronostratigraphic tool a sequence of radiocarbon dated holocene interdune strata permit optical dating of the intercalated dune sand to be tested the concordance is good the optical dates for the aeolian deposits not datable by radiocarbon suggest that aeolian sedimentation at clear creek peaked during two relatively short phases at ca 8500 and 4000 yr b p the dates indicate that aeolian accumulation maxima at least in the clear creek area may not be synchronous with previously defined phases of marked aridity

optical dating of dune sand for the study of sea level change a new widely applicable method to obtain well constrained relative sea level records presented here relies on optical dating of inorganic coastal landforms and sediments eighteen optical ages of basal dune sand from a barrier in massachusetts united states indicate that local relative sea level rose 8 m during the past 5 5 k y a sea level curve drawn from these optical ages shows good agreement with independent evidence from salt marsh peat sampled behind the barrier demonstrating the reliability of the method optical dating will be particularly useful in analyzing coastal records that contain too few organic indicators to allow high resolution 14 c based analyses

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

a 750 year fire history based on lake sediment records in central yellowstone national park usa a 750 year fire history was reconstructed for the central plateau of yellowstone national park from the deep water sediments of five lakes the charcoal record from a large lake provided a chronology of regional fires data from four small lakes were used to study local and extralocal fires the co occurrence of abundant charcoal and high magnetic susceptibility values at the same stratigraphic level was used as evidence of a local catchment fire and a charcoal peak without high magnetic susceptibility was ascribed to an extralocal fire or a local fire without a related erosion event the fire history was compared with the dendrochronologic fire record for the last 450 years and the close agreement provided the justification to extend the chronology back in time large areas of the region burned in ad 1988 c 1700 c 1560 and c 1440 from c 1220 to 1440 and c 1700 to 1987 intermediate to small areas burned the near absence of fires in the twentieth century prior to the large fires of 1988 is evi