stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

loess sedimentation in tibet provenance processes and link with quaternary glaciations abstract well preserved loess deposits are found on the foothills of mountains along the middle reaches of the yarlung zangbo river in southern tibet optically stimulated luminescence osl dating is used to determine loess ages by applying the single aliquot regeneration technique geochemical mineralogical and granulometric measurements were carried out to allow a comparison between loess from tibet and the chinese loess plateau our results demonstrate that i the loess deposits have a basal age of 13 11 ka suggesting they accumulated after the last deglaciation ii loess in southern tibet has a glacial origin resulting from eolian sorting of glaciofluvial outwash deposits from braided river channels or alluvial fans by local near surface winds and iii the present loess in the interior of tibet has accumulated since the last deglaciation when increased monsoonal circulation provided an increased vegetation cover that was sufficient for trapping eolian silt the lack of full glacial loess is either due to minimal vegetation cover or possibly due to the erosion of loess as glaciofluvial outwash during the beginning of each interglacial such processes would have been repeated during each glacial interglacial cycle of the quaternary

geochemical variations in peoria loess of western iowa indicate paleowinds of midcontinental north america during last glaciation peoria loess deposited in western iowa during the last glacial maximum lgm shows distinct geochemical and particle size variations as a function of both depth and distance east of the missouri river geochemical and particle size data indicate that peoria loess in western iowa probably had two sources the missouri river valley and a source that lay to the west of the missouri river both sources indicate that lgm paleowinds in western iowa had a strong westerly component similar to interpretations of previous workers a compilation of loess studies in iowa and elsewhere indicates that westerly winds were dominant during loess transport over much of the midcontinent south of the laurentide ice sheet which is not in agreement with paleowinds simulated by atmospheric general circulation models agcms agcms consistently generate a glacial anticyclone with easterly or northeasterly winds over the laurentide ice sheet and the area to the south of it loess deposition in the midcontinent during the lgm may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial anticyclone

origin of loess deposits in the north tian shan piedmont central asia abstract loess deposits are widely distributed along the mountain piedmonts of central asia the transport processes and origins of central asian loess sediments remain poorly understood here we investigate the origin and formation of loess along the northern piedmont of the tian shan based on trace element including rare earth element ratios and multidimensional scaling analysis our results indicate that the loess has undergone weak chemical weathering using a selection of geochemical fingerprinting techniques based on pearson correlation and kruskal wallis h tests we establish a genetic link between alluvial proluvial fans plains deserts and loess along the tian shan piedmont in northern kyrgyzstan and southern kazakhstan the unsorted sediments on the piedmont slopes and alluvial proluvial plains are common sources for both deserts and loess to the north of the tian shan dune sediments are not the main source of the fine grained loess origin and formation of central asian loess is strongly dependent on local topographic context and wind dynamics only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made

pseudogleyed loess derivates the most common soil parent materials in the pannonian region of croatia abstract loess derived sediments represent the most widespread soil parent materials in the pannonian region of croatia pseudogley as the most common soil type in this region developed mainly on such parent materials pseudogleys largely correlate with the wrb reference soil group of stagnosols on the general soil map of croatia at scale 1 50 000 gsm of croatia the distinction is made between pleistocene loams pl and loess as pseudogley parent materials the initial purpose of this research was to investigate if the criteria for this distinction were clear and consistent and if the terms used for labeling these parent materials were adequate hence we investigated parent materials of 18 pseudogleys across 6 different locations three on loess and three on pl in the pannonian region of croatia we analyzed their morphology including micromorphology of three representative parent materials particle size distribution total porosity ph and mineral assemblages by modal analysis of three representative parent materials following these analyses no systematic differences between the loess parent materials and the pl parent materials were found additionally it was concluded that due to significant geogenetic and or pedogenetic alterations of all studied parent materials none of them should be labeled simply as loess hence parent material at one location was labeled as leached loess derivate and parent materials at all other locations were labeled as pseudogleyed loess derivates both types of parent materials were described in detail and defined in addition the terminology and the classification of loess derived parent materials in general was proposed the analyzed pseudogleyed loess derivates were not completely uniform across the investigated locations primarily this was due to the polygenesis of loess reflected by differences in particle size distributions and compositions of light and heavy mineral fractions secondarily it was due to the 600 1100 mm map gradient along the study region reflected by differences in ph values and properties of redoximorphic features although pedogenesis of the investigated parent materials might have started already during the late glacial and have continued throughout the holocene at varying and overall decreasing rates their morphology indicates that pseudogleization and lessivage are still active processes which occur simultaneously in the analyzed parent materials and agree with the present climate

characterizing large river history with shallow geophysics middle yukon river yukon territory and alaska abstract changes in longitudinal valley fill thickness can provide inferences about fluvial behaviour over millennia increased thickness of channel deposits may reveal climate induced accelerated sediment supply basin subsidence tectonic displacements or rising downstream base level decreases in thickness expressed as terraces may suggest active uplift decreased sediment flux or falling base level within a reach to date methods to characterize valley fills have depended largely on borehole data however recent developments in shallow geophysics make such investigations possible and provide a practical methodology to investigate alluvial rivers we carried out a longitudinal geophysical survey coupled with floodplain chronologies to characterize a 1000 km reach of the middle yukon river between western yukon territory and central alaska ground penetrating radar gpr and electrical resistivity ground imaging ergi profiles along the middle yukon river between central yukon and alaska coupled with channel bottom echo profiles demonstrates that there is little variation in thickness of gravel fill and depth of active scour holes gpr surveys near the white river the largest sediment source in the upper yukon show no significant longitudinal variation in gravel thickness 8 16 m up to near circle alaska 530 km of wandering channels geophysical profiles across the yukon flats sedimentary basin 430 km of braided and wandering channels show an increase in gravel thickness 25 30 m but this is consistent with compaction of underlying lacustrine sediment and maximum depths of contemporary scour holes from the western margin of the yukon flats to the dalton highway bridge 30 km confined valley with no floodplain or braid bars borehole data at the bridge indicates 6 10 m of gravel on bedrock beneath 3 6 m of water floodplain stratigraphy indicates there is little evidence of fluvial aggradation of the middle yukon during the holocene radiocarbon ages from the gravel overbank silt contact near present river level demonstrate a general vertical stability of the river with a period of rapid eolian accumulation during the late pleistocene and early holocene the consistency of gravel fill and scour hole depth and lack of holocene terraces along the 1000 km reach of the yukon indicate that the river has been in a state of mass balance equilibrium of sediment transport input output over the holocene despite massive sediment influxes from the glacial fed white river and crossing major faults variation in valley fill depth is not significant and further the yukon flats reach shows no evidence of bed aggradation during the pleistocene and has probably existed in equilibrium since the late pliocene

eolian grain size signature of the sikouzi lacustrine sediments chinese loess plateau implications for neogene evolution of the east asian winter monsoon in order to explore the neogene evolution of east asian winter monsoon circulation grain size analysis was conducted on the neogene sikouzi section guyuan ningxia china a relatively monsoon sensitive region the results show that most of the particles are fine the sand bearing samples median grain size md 63 m are less than 6 4 and that all the grain size distribution curves of representative samples have a similar pattern to those of eolian dust sediments on the chinese loess plateau rare earth element ree patterns of eight samples from the sikouzi section are all characterized by light l ree enrichments relatively flat heavy h ree patterns and slight negative eu anomalies similar to those of loess and the average upper continental crust these lines of evidence point to a windblown origin of the sikouzi fine sediments based on previous studies the 10 70 m fraction of the sikouzi sediments is mainly transported by the east asian winter monsoon and an increase in content of the 10 70 m fraction reflects strengthening of the winter monsoon in contrast sand grains in samples of md 63 m are probably brought into the study area by rivers and streams linked with precipitation enhancement according to stratigraphic variations in content of various fractions of the sikouzi grain size record the neogene evolution of the east asian monsoon circulation can be divided into three stages during the period 20 1 12 0 ma the 10 70 m fraction holds the lowest values whereas sand content usually shows high percentages denoting a weak winter monsoon and a strong summer monsoon after 12 0 ma the 10 70 m fraction increased substantially and remained at high values while sand content showed a marked decline indicating that the winter monsoon strengthened dramatically and the summer monsoon declined significantly from 4 3 to 0 07 ma the winter monsoon strengthened further as evidenced by the gradual increase in content of the 10 70 m fraction this inference agrees well with the timing of glaciation development in the northern hemisphere during the early to middle miocene the high values of both md and sand content are mainly distribute in five intervals 19 8 18 8 ma 18 0 17 5 ma 16 7 15 6 ma 14 3 13 7 ma and 13 0 12 0 ma corresponding to five periods of intense precipitation the interval from 16 7 to 15 6 ma is well correlated with the middle miocene climatic optimum determined by the well known miocene shanwang biota from eastern china as for the other four periods it is speculated that episodic growth of the east antarctic ice sheet possibly shifted atmospheric fronts such as the intertropical convergence zone itcz and thus carried water vapor further northward leading to increases in regional precipitation on the northern midlatitude continent including north china

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

meteorological controls on wind erosion during foehn wind events in the eastern southern alps new zealand foehn winds in the lee of mountain barriers create highly favourable meteorological conditions for wind erosion in alpine areas and over adjacent lowlands this paper presents meteorological observations made during winter and summer foehn wind erosion events as part of a 3 year investigation into the physical nature and incidence of eolian processes in the eastern southern alps new zealand foehn winds were observed to initiate eolian activity including dust storm genesis when mean near surface wind speeds exceeded 7 8 m s 1 over a 20 min period in the absence of precipitation wind speeds of 25 30 m s 1 were frequently recorded during typical foehn events and wind speed maxima of 40 50 m s 1 were monitored during severe foehn windstorms saltation clouds sampled at 0 5 and 1 m above glaciofluvial deposits during foehn wind erosion events were found to display a mean grain size of between 300 and 435 m the entrainment of fine grained surface sediments by the airstream appeared to be enhanced in late autumn may and early spring september by freeze thaw cycles that were observed to result in needle ice growth in exposed glaciofluvial and lacustrine deposits the needle ice fragmented such deposits producing surfaces that were aerodynamically rough and highly susceptible to deflation by the airstream following a thaw observations made by this study are thought to be similar to foehn wind erosion events reported in the lee of other substantial mountain ranges such as the rocky mountains andes hindu kush and karakoram

absence of glaciation in illinois during marine isotope stages 3 through 5 a10be inventory and14c ages of material from a core from northernmost illinois support previous interpretations that this area was ice free from ca 155 000 to 25 000 yr ago during much of this period from about 155 000 to 55 000 yr ago 10be accumulated in the argillic horizon of the sangamon geosol wisconsinan loess containing inherited10be was deposited above the sangamon geosol from ca 55 000 to 25 000 yr ago and was subsequently buried by late wisconsinan till deposited by the lake michigan lobe of the laurentide ice sheet the sangamonian interglacial stage has been correlated narrowly to marine oxygen isotope substage 5e our data indicate instead that the sangamon geosol developed during late stage 6 all of stages 5 and 4 and early stage 3

spatial variations of sr nd isotopic ratios mineralogical and elemental compositions of cryoconite in an alaskan glacier to understand the geological origins of minerals in cryoconite and the nutrients sources for microbes on glaciers we analyzed the sr nd isotopic ratios of the four mineral fractions in cryoconites including saline carbonate phosphate silicate and the organic fraction obtained from gulkana glacier in alaska the isotopes in the silicate mineral fraction exhibited spatial variation within the glacier 87sr 86sr 0 704533 0 709563 end 0 16 0 to 0 5 which can be explained by the different mixing ratios of the two distinct sources one of the sources is lateral and terminal moraines or soil and the other is the medial moraine of the glacier the minerals in the cryoconite at the lower sites in the glacier are likely derived from the former source whereas those at the upper sites are from latter sources the mineralogical and elemental compositions also support mixing of the silicate minerals from the two local sources the sr isotopic ratios of the organic fraction also showed spatial variation on the glacier in the middle sites a trend similar to those of the phosphate fraction the results suggest that the organic matter is mostly the byproducts of microbes using the phosphate minerals as a nutrient source

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

aeolian dust transport and deposition by foehn winds in an alpine environment lake tekapo new zealand abstract observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identify principle sources of wind blown dust within an alpine lake basin meteorological observations made throughout the study indicate that foehn windstorms provide ideal conditions for the initiation of aeolian processes including dust storm genesis a mean wind speed during foehn windstorms of 7 5 m s 1 at 2 65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active areas within the lake basin particularly from the dry braid channels of glacier fed rivers exposed lacustrine deltas and degraded tussock grasslands this threshold entrainment velocity is similar to others presented within the international literature for such surface types a diurnal modulation of meteorological parameters monitored during foehn wind events suggests that aeolian processes such as dust entrainment are most likely to occur from late morning to early evening however where topography enhances wind speeds for example by channelling airflow down river valleys favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation potential dust roses were determined for two sites within the lake basin the dust roses supported anecdotal and observational evidence of principle dust sources within the study area and appear to be an effective tool for identifying the potential hazard to a particular location from blowing dust once the physical trigger conditions for dust entrainment are known this requires detailed and concurrent monitoring of meterological variables in association with dust transportation and deposition rates especially in complex terrain where many micro climates often exist

geochemical characterization and origin of southeastern and eastern european loesses serbia romania ukraine abstract the loess paleosol sections of batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine were geochemically characterized based on discriminant analysis of major and trace elements the ratios of al ti fe ti and al fe the a cn k ternary plot and element enrichment depletion relative to the average composition of the upper continental crust the origin of the loess material in the southern pannonian basin vojvodina the lower danube basin dobrudja and the dnieper area was evaluated by comparison with the representative element composition of possible source areas and by considering the geomorphodynamic setting also the background values of the initial magnetic susceptibility of the loesses were taken into account for the lower danube basin dobrudja and the ukraine paleowind direction was reconstructed based on the geographic distribution of sandy soil texture and dunes related to river systems finally loesses were evaluated as possible samples of the average upper continental crust our results show that danube and dnieper loess areas can be clearly distinguished the former reveal higher al and fe contents the latter higher si zr hf content and indications of effective mineral and grain size sorting we can confirm that vojvodina loess originated from danube alluvial material and loess of the dnieper area from glaciofluvial sediments of the fennoscandinavian ice sheet the dobrudja loess derived also predominantly from danube alluvium but shows significant contribution of a second loess source probably the glaciofluvial sediments of the ukraine this was forced by northerly katabatic winds from the fennoscandinavian ice sheet whereas wnw winds prevailed in the western walachian plain the studied loesses reflect the average composition of the upper continental crust yet biases exist due to selective mineral element enrichment and depletion in the course of previous sedimentary recycling phases respectively material of all studied loess deposits seems to derive originally from sedimentary rocks

change in atmospheric mineral aerosols in response to climate last glacial period preindustrial modern and doubled carbon dioxide climates desert dust simulations generated by the national center for atmospheric research s community climate system model for the current climate are shown to be consistent with present day satellite and deposition data the response of the dust cycle to last glacial maximum preindustrial modern and doubled carbon dioxide climates is analyzed only natural non land use related dust sources are included in this simulation similar to some previous studies dust production mainly responds to changes in the source areas from vegetation changes not from winds or soil moisture changes alone this model simulates a 92 33 and 60 change in dust loading for the last glacial maximum preindustrial and doubled carbon dioxide climate respectively when impacts of carbon dioxide fertilization on vegetation are included in the model terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions probably due to the lack of simulation of glaciogenic dust sources in order to include the glaciogenic dust sources as a first approximation we designate the location of these sources and infer the size of the sources using an inversion method that best matches the available data the inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2 1 to 3 3 times current deposition

variations in trace element including rare earth element concentrations with grain sizes in loess and their implications for tracing the provenance of eolian deposits the concentrations of rare earth elements rees and other 28 trace elements were determined in seven grain size fractions from four loess samples collected from the tibetan plateau the sichuan basin and the chinese loess plateau the results indicate that concentrations of rees except for heavy rare earth elements hrees are almost grain size independent however rees show clear fractionation with grain size middle rare earth element mree depletion increases with decreasing grain size whereas hree enrichment increases with decreasing grain size excluding rees and y most of the other trace element concentrations tend to increase with decreasing grain sizes the trace element geochemistry indicates that the potential sources of eolian deposits from the sichuan basin the chinese loess plateau and the tibetan plateau differ from one another this comparative study confirmed that the eolian materials from the asian continent are the source of the terrigenous component of the central north pacific sediments and the loess from the chinese loess plateau could represent the average composition of eolian dust from the asian continent in contrast the eolian deposits in the sichuan basin and in the tibetan plateau are mainly of local origin with short distance eolian transport

geochemistry of the xining xifeng and jixian sections loess plateau of china eolian dust provenance and paleosol evolution during the last 140 ka abstract loess and paleosol samples from three distant sections xining xifeng jixian of the chinese loess plateau were analyzed for chemical and nd sr isotopic compositions in order to obtain information about the paleoclimatic variation during the last 140 ka these three sections represent three different climatic conditions from arid in the west xining to more humid in the east jixian across the loess plateau isotopic analyses show that all the three sections display a restricted range of 143 nd 144 nd ratios or e nd 10 0 5 indicating the dominance of relatively young and uniform upper crustal sources for the eolian dust the loess and paleosol samples have typical upper crustal 87 sr 86 sr ratios 0 714 0 718 and their variation can partly be attributed to different carbonate silicate ratios in the samples ree data from the three sections are indistinguishable from each other they show typical upper crust patterns characterized by la yb n 10 and eu eu 0 65 the high degree of chemical and isotopic homogeneity suggests that the dust source region must have undergone multiple recycling and thorough sedimentary mixing processes various chemical indicators have been used to monitor the pedogenetic intensity in these sections although results for the jixian section agree reasonably well with the known climatic conditions on the loess plateau the other two sections yield results not in agreement with some well accepted proxies like magnetic susceptibility or grain size distribution some chemical proxy indicators established in our previous work on the luochuan section such as the systematic u depletion and negative ce anomalies in ree patterns in soils are not clearly recorded in the present case the discrepancy between different climatic proxies could be related to the effective soil water budget temperature as well as the rate of development of each proxy

a 3 m y record of pliocene pleistocene loess in interior alaska many distal tephra beds exist in the thick fossiliferous loess deposits near fairbanks interior alaska isothermal plateau fission track ages determined on glass shards from tephra beds in conjunction with tephrostratigraphic and magnetostratigraphic techniques indicate that loess deposition began in the late pliocene an antiquity previously unsuspected hence there is the opportunity now to reconstruct a detailed well dated record of environmental changes in interior alaska during the past 3 m y

late quaternary loess in northeastern colorado part ii pb isotopic evidence for the variability of loess sources a new application of the pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late wisconsin loess in the central great plains of eastern colorado samples of the peoria loess collected throughout the study area contain k feldspar derived from two isotopically and genetically distinct sources 1 glaciogenic material from early and middle proterozoic crystalline rocks of the colorado province and 2 volcaniclastic material from the tertiary white river group exposed on the northern great plains pb isotopic compositions of k feldspar in loess from two dated vertical sections at beecher island and last chance colorado vary systematically implying climatic control of source availability we propose a model whereby relatively cold conditions promoted the advance of front range valley glaciers discharging relatively little glaciogenic silt but strong winds caused eolian erosion of white river group silt due to a decrease in vegetation cover during warmer periods valley glaciers receded and discharged abundant glaciogenic silt while surfaces underlain by the white river group were stabilized by vegetation isotopic data from eastern colorado loess sections record two warm cold warm cycles during late wisconsin time between about 21 000 and 11 000 radiocarbon yr b p similar to results from other studies in the united states and greenland

geochemical evidence for african dust and volcanic ash inputs to terra rossa soils on carbonate reef terraces northern jamaica west indies abstract the origin of red or reddish brown clay rich terra rossa soils on limestone has been debated for decades a traditional qualitative explanation for their formation has been the accumulation of insoluble residues as the limestone is progressively dissolved over time however this mode of formation often requires unrealistic or impossible amounts of carbonate dissolution therefore where this mechanism is not viable and where local fluvial or colluvial inputs can be ruled out an external source or sources must be involved in soil formation on the north coast of the caribbean island of jamaica we studied a sequence of terra rossa soils developed on emergent limestones thought to be of quaternary age the soils become progressively thicker redder more fe and al rich and si poor with elevation furthermore although kaolinite is found in all the soils the highest and oldest soils also contain boehmite major and trace element geochemistry shows that the host limestones and local igneous rocks are not likely source materials for the soils other trace elements including the rare earth elements ree show that tephra from central american volcanoes is not a likely source either however trace element geochemistry shows that airborne dust from africa plus tephra from the lesser antilles island arc are possible source materials for the clay rich soils a third as yet unidentified source may also contribute to the soils we hypothesize that older more chemically mature jamaican bauxites may have had a similar origin the results add to the growing body of evidence of the importance of multiple parent materials including far traveled dust to soil genesis

a late pleistocene glacial chronology for the southern brooks range stratigraphic record and regional significance radiocarbon dates from 11 measured sections in the koyukuk region provide a chronology of the last pleistocene glaciation glaciers were advancing strongly by 24 000 yr ago they built moraines near the south flank of the brooks range retreated briefly about 22 000 to 20 000 yr b p then readvanced at least one more time into their terminal zones glaciation was accompanied by alluviation of the koyukuk and kobuk drainage systems and by periglacial processes that resemble those taking place today farther north and at higher altitudes moraines near the south flank of the range were being revegetated by 13 500 yr b p a strong final readvance into end moraine belts of some northern valleys occurred about 13 000 to 12 500 yr ago and this event may be synchronous with less extensive glacier readvances in upper valleys of the koyukuk region upper valleys were largely deglaciated by 11 800 yr b p dated stratigraphic sections from the northern alaska range show similar ages for initiation and close of glaciation and also suggest a possible interstadial episode about 20 000 yr ago scanty records of fluctuations during ice wastage probably reflect the general scarcity of datable wood peat and organic soils between about 19 500 and 13 500 yr ago the brooks range and alaska range chronologies closely approximate glacial successions determined else where in eastern beringia and in siberia advance and retreat of glaciers throughout this region evidently were associated with widespread climatic changes that also controlled the late wisconsin history of the laurentide ice sheet the itkillik ii and late itkillik phases of former usage are part of a single glaciation that was entirely separate from the preceding itkillik i ice advance for this reason the local term walker lake glaciation is here extended to the last major glaciation of the entire southern brooks range and use of itkillik phases should be discontinued the term itkillik glaciation is hereby restricted to the next older ice advance in accord with its original definition cold and dry conditions during the last glaciation of eastern beringia are indicated by 1 relatively small mountain glaciers 2 slight 200 m depression of glaciation limits below modern values 3 periglacial features indicating severe frost action on slopes with little protective plant cover 4 widespread accretion of eolian sand 5 low pollen influx rates 6 scarcity of radiocarbon datable organic remains and 7 general absence of carbonaceous paleosols plant growth may have been much more restricted than generally believed with relatively low capacity to support grazing animals and human hunting bands

desert loess versus glacial loess quartz silt formation source areas and sediment pathways in the formation of loess deposits abstract pathways are presented which show the proposed sequence of events involved in the formation of loess deposits both hypothetical deposits and those of central china hungary nigeria and tunisia these pathways illustrate the potential role of and inter relationships between a variety of silt generating mechanisms in the formation of loess using these pathways the existence of desert loess is discussed and it is concluded that this depends on how the terms glacial loess and desert loess are applied if desert loess is taken either to signify nonglacial mechanisms of silt production or to characterise the environment from which aeolian entrainment took place then desert loess is a very real and widely distributed deposit however if the term glacial loess is used to refer to the global climatic regime under which the loess deposit has formed rather than the geomorphic mechanisms responsible for silt generation then desert loess would not be an appropriate term for the classification of loess deposits it is suggested that classifying loess deposits with reference to the global climatic regime under which they accumulated would facilitate a greater understanding of the role of environmental conditions at all stages in the formation of loess deposits

optically stimulated luminescence dating of late quaternary loess deposits in the coastal region of north china provenance and paleoclimatic implications abstract the aeolian deposits in the coastal region of north china are important for reconstructing paleoclimate in this paper chronology climatic proxies and chemical compositions of four loess sections were studied optically stimulated luminescence osl dating results indicate that the coastal loess was accumulated during late quaternary with ages ranging from the penultimate glacial period to the latest holocene both granulometric characteristics and geochemical properties indicate that the dust provenance of the coastal loess is partially different from that of the chinese loess plateau characterized by more proximal contributions except distal dust transported by northwesterly winter winds from the inland gobi and sand deserts the coastal loess also contains proximal local coarse particles which were derived from the exposed shelf as well as neighboring hills multiple climatic proxies including color magnetic susceptibility and particle size parameters correlate well with the marine specmap 18o record indicating that climatic changes in the coastal region of north china during the late quaternary was mainly controlled by variations of the east asian monsoon driven by changes in global ice volumes

geochemical evidence for airborne dust additions to soils in channel islands national park california there is an increasing awareness that dust plays important roles in climate change biogeochemical cycles nutrient supply to ecosystems and soil formation in channel islands national park california soils are clay rich vertisols or alfi sols and mollisols with vertic properties the soils are overlain by silt rich mantles that contrast sharply with the underlying clay rich horizons silt mantles contain minerals that are rare or absent in the volcanic rocks that dominate these islands immobile trace elements sc th la and ta nd cr and rare earth elements show that the basalt and andesite on the islands have a composition intermediate between upper continental crust and oceanic crust in contrast the silt fractions and to a lesser extent clay fractions of the silt mantle have compositions closer to average upper continental crust and very similar to mojave desert dust island shelves exposed during the last glacial period could have provided a source of eolian sediment for the silt mantles but this is not supported by mineralogical data we hypothesize that a more likely source for the silt rich mantles is airborne dust from mainland california and baja california either from the mojave desert or from the continental shelf during glacial low stands of sea although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin the eolian silt mantles constitute an important medium of plant growth and provide evidence that abundant eolian silt and clay may be delivered to the eastern pacifi c ocean from inland desert sources

late quaternary loess like paleosols and pedocomplexes geochemistry provenance and source area weathering manasbal kashmir valley india abstract the late quaternary loess and loess like deposits in kashmir valley are natural archives that have preserved paleoclimate and paleoenvironmental records of the region we present a loess like paleosol located along the margin of the manasbal lake ganderbal which was studied in detail for understanding the pedological processes and reconstructing the late quaternary soil formation in this paper we present loess like paleosol formation of a nearly 10 6 m thick sequence exposed along the margin of manasbal lake ganderbal district srinagar kashmir geochemical and textural data of this loess like sedimentary sequence fluctuate reflecting the varied depositional processes operating in the valley differential intensity of weathering and processes of pedogenesis weathering indices such as chemical index of alteration chemical index of weathering and plagioclase index of alteration reveal weak to moderate weathering of the parent material provenance discrimination diagrams of the present study disclose that the manasbal loess like paleosol sediments are derived from the mixed source rocks suggesting a variety of provenance with variable geological settings which apparently have undergone weak to moderate recycling processes the manasbal paleosol horizons have been dated by the optically stimulated luminescence osl method to the marine isotope stages mid mis 3 41 7 8 0 ka and late mis 2 14 6 3 8 ka during the mis 3 period the climate was wetter forming a strong ahbtk paleosol as inferred from the geochemical data a steady increase in the caco 3 content and c n ratio in the paleosols from 6 50 m mis 3 indicates arid and drier climatic conditions the area around manasbal lake incised because of climate change and neotectonic activity since post 14 ka

cryostratigraphy of late pleistocene syngenetic permafrost yedoma in northern alaska itkillik river exposure abstract extremely ice rich syngenetic permafrost or yedoma developed extensively under the cold climate of the pleistocene in unglaciated regions of eurasia and north america in alaska yedoma occurs in the arctic foothills the northern part of the seward peninsula and in interior alaska a remarkable 33 m high exposure along the lower itkillik river in northern alaska opened an opportunity to study the unmodified yedoma including stratigraphy particle size distribution soil carbon contents morphology and quantity of segregated wedge and thermokarst cave ice the exposed permafrost sequence comprised seven cryostratigraphic units which formed over a period from 48 000 to 5 000 14c yr bp including 1 active layer 2 intermediate layer of the upper permafrost 3 4 two yedoma silt units with different thicknesses of syngenetic ice wedges 5 buried peat layer 6 buried intermediate layer beneath the peat and 7 silt layer with short ice wedges this exposure is comparable to the well known mus khaya and duvanny yar yedoma exposures in russia based on our field observations literature sources and interpretation of satellite images and aerial photography we have developed a preliminary map of yedoma distribution in alaska

biogeochemistry of glacial landscape systems abstractglaciers affect biogeochemistry of landscapes through their sediments glacial erosion rates are high and the sediments produced are distinctively fine grained hence glaciers can be thought of as producers of mineral surface area although this mineral surface area is highly reactive temperature limits chemical weathering fluxes from glaciers and their surroundings more significant effects may be associated with silt deposited in loess and on continental margins thick deposits in both settings contribute to carbon cycling through both silicate weathering and organic carbon burial the impact of glaciers on biogeochemical cycles will be long lasting as the legacy of glacial erosion processes continues as long as sediment yields are elevated

tephrochronology of late cenozoic loess at fairbanks central alaska nineteen distinctive distal tephra beds from the gold hill loess in the fairbanks region central alaska are divided into two groups based on their color mineralogy glass shard morphology and the major and trace element composition of their glass shards this dichotomy in tephra composition is believed to reflect the two source regions namely the eastern aleutian arc alaska peninsula region and the wrangell volcanic field despite the fragmentary nature of the preserved loess record which contains many local unconformities these tephra beds can be used to link the numerous loess exposures in the fairbanks region in their proper time sequence establishing thereby a comprehensive reliable time stratigraphic framework because these distal tephra beds are related to large magnitude volcanic eruptions given the long distance to the nearest possible source vent they will also enable correlation of the late cenozoic sedimentary sequence at fairbanks to those of adjacent regions of alaska and the yukon tephra beds with bubble wall or chunky glass shards have been dated by the isothermal plateau fission track method results demonstrate that the gold hill loess spans a long interval of time from late pliocene time to the last interglacial about 125 ka however the age of the basal part of this formation is not well constrained due to the apparent absence of tephra beds paleomagnetic studies suggest that loess deposition in the fairbanks region began about 3 ma

the rosa keystone dunes field the geoarchaeology and paleoecology of a late quaternary stabilized dune field in eastern beringia stabilized sand sheets and dunes hold a remarkable amount of information on paleoenvironmental conditions under which late quaternary landscapes evolved in northern subarctic regions we provide the results of a project focused on understanding the development of lowland environments and ecosystems including dunes and sand sheets which were critical habitat for early human occupations in subarctic regions our study area is the rosa keystone dunes field in the shaw creek flats of the middle tanana river basin interior alaska one of the oldest continuously occupied areas in north america 14 000 cal bp to present the disturbance regimes of reactivated dunes and associated forest fire cycles between 12 500 and 8800 cal bp fostered a unique early to mid successional mixed vegetation community including herbaceous tundra shrubs and deciduous trees this environment provided key habitats for large grazers and browsers significant resources for early hunter gatherer populations in central alaska aft

late pleistocene dust dynamics and pedogenesis in southern eurasia detailed insights from the loess profile toshan ne iran abstract in southern eurasia recurrent phases of aridization dust source extension and enhanced aeolian sedimentation alternated with moister intervals promoting reduced deflation areas and dust accumulation in the context of late pleistocene climate changes weathering and soil forming intensity in this greater region are hence mainly governed by fluctuations in the balance between dust supply and moisture availability among the hitherto known sections the toshan loess soil sequence lps represents a key site due to the quality of the record and the multitude of available data giving detailed insights into the timing and magnitude of dust accumulation and soil formation of the region to elucidate these dynamics for much of the past 130 000 years bulk mineralogical and geochemical data are presented supplemented by a high resolution magnetic susceptibility record and by the results of a detailed micromorphological study of loess at toshan the last interglacial luvisol phaeozem like mis 5e and the early glacial interstadial steppic palaeosols mis 5 c and a are characterized by gradually increasing grain size and decreasing degrees in decomposition of micaceous and mafic minerals pronounced feldspar weathering is detected in the last interglacial and modern soils only which formed under reduced or absent dust deposition on penultimate and last glacial loess respectively postsedimentary the overall pedosedimentary conditions correspond to large scale trends of increasing drought dust accumulation and wind strength in southern eurasia in relation to decreasing moisture availability towards the early pleniglacial mis 4 causing soil formation under ongoing dust deposition synsedimentary similar intervals of synsedimentary soil formation are recorded during the interglacial interstadial stadial transitions of the early glacial and during pleniglacial mis 4 to 2 interstadials the latter are marked by gradual increases in magnetic susceptibility colour and decreasing texture conversely silicate weathering could not be detected suggesting that grain size fluctuations are a primary feature thus windy and arid pleniglacial conditions in southern eurasia were interrupted by intermittent phases of synsedimentary soil formation in response to short lived and relatively moist interstadials although the interrelation of these incipient soils throughout southern eurasia is afflicted with considerable restrictions the oscillatory pattern of the toshan lps bears great similarity with millennial scale oscillations recorded in limnic archives of western asia

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

geochemistry of loess paleosol sediments of kashmir valley india provenance and weathering abstract middle to late pleistocene loess paleosol sediments of kashmir valley india were analyzed for major trace and ree elements in order to determine their chemical composition provenance and intensity of palaeo weathering of the source rocks these sediments are generally enriched with fe 2 o 3 mgo mno tio 2 y ni cu zn th u sc v and co while contents of sio 2 k 2 o na 2 o p 2 o 5 sr nb and hf are lower than the ucc chondrite normalized ree patterns are characterized by moderate enrichment of lrees relatively flat hree pattern gd cn yb cn 1 93 2 31 and lack of prominent negative eu anomaly eu eu 0 73 1 01 average 0 81 paas normalized ree are characterized by slightly higher lree depleted hree and positive eu anomaly various provenance discrimination diagrams reveal that the kashmir loess paleosol sediments are derived from the mixed source rocks suggesting large provenance with variable geological settings which apparently have undergone weak to moderate recycling processes weathering indices such as cia ciw and pia values 71 87 83 83 and 80 57 respectively and a cn k diagram imply weak to moderate weathering of the source material

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

eolian deflation by ancient katabatic winds a late quaternary example from the north alaska range strong katabatic winds are frequently generated in glaciated mountain valleys of the alaska range by downglacier gravitational flow of chilled air stronger katabatic winds probably occurred during late quaternary time when glaciers were more extensive and such winds may have greatly influenced eolian sedimentation in nenana river valley and in most of adjacent teklanika river valley the entire 1 to 2 m thick eolian cap is postglacial in age and the beginning of loess deposition coincides almost exactly with rapid recession of late wisconsin ice previously deposited loess and bluff edge dunes were apparently deflated during the last glaciation between 25 000 and 12 000 yr b p loess deposition in these mountain valleys thus is exclusively an interglacial phenomenon glacial phases are characterized by deflation meteorological modeling of katabatic winds generated during the last glaciation predicts that paleowind velocities greatly exceeded the entrainment thresholds required for eolian deflation when both nenana river and teklanika river valleys are compared theoretical differences in the potential for generating katabatic winds and differences in valley physiography explain why pre holocene loess is preserved in downstream reaches of teklanika river valley and not nenana river valley the presence of strong katabatic winds in mountain valleys beyond former glacier limits has significant implications for late pleistocene paleoecology and archeology

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

quantitative mineralogy of the yukon river system changes with reach and season and determining sediment provenance the mineralogy of yukon river basin sediment has been studied by quantitative x ray diffraction bed beach bar and suspended sediments were analyzed using the rockjock computer program the bed sediments were collected from the main stem and from selected tributaries during a single trip down river from whitehorse to the yukon river delta during the summer of 2001 beach and bar sediments were collected from the confluence region of the tanana and yukon rivers during the summer of 2003 suspended sediments were collected at three stations on the yukon river and from a single station on the tanana river at various times during the summers of 2001 through 2003 with the most complete set of samples collected during the summer of 2002 changes in mineralogy of yukon river bed sediments are related to sediment dilution or concentration effects from tributary sediment and to chemical weathering during transport carbonate minerals compose about 2 wt of the bed sediments near whitehorse but increase to 14 wt with the entry of the white river tributary above dawson thereafter the proportion of carbonate minerals decreases downstream to values of about 1 to 7 wt near the mouth of the yukon river quartz and feldspar contents of bed sediments vary greatly with the introduction of pelly river and white river sediments but thereafter either increase irregularly quartz from 20 to about 50 wt or remain relatively constant feldspar at about 35 wt with distance downstream clay mineral content increases irregularly downstream from about 15 to about 30 wt the chief clay mineral is chlorite followed by illite smectite there is little to no kaolinite the total organic carbon content of the bed sediments remains relatively constant with distance for the main stem generally 1 to 2 wt with one exception but fluctuates for the tributaries 1 to 6 wt the mineralogies of the suspended sediments and sediment flow data were used to calculate the amount of mineral dissolution during transport between eagle and pilot station a distance of over 2000 km we estimate that approximately 3 wt of the quartz 15 wt of the feldspar 1 wt of the alkali and 25 wt of the plagioclase and 26 wt of the carbonates 31 wt of the calcite and 15 wt of the dolomite carried by the river dissolve in this reach the mineralogies of the suspended sediments change with the season for example during the summer of 2002 the quartz content varied by 20 wt with a minimum in mid summer the calcite content varied by a similar amount and had a maximum corresponding to the quartz minimum these modes are related to the relative amount of sediment flowing from the white river system which is relatively poor in quartz but rich in carbonate minerals suspended total clay minerals varied by as much as 25 wt with maxima in mid july and suspended feldspar varied up to 10 wt suspended sediment data from the summers of 2001 and 2003 support the 2002 trends a calculation technique was developed to determine the proportion of various sediment sources in a mixed sediment by unmixing its quantitative mineralogy results from this method indicate that at least three sediment sources can be identified quantitatively with good accuracy with this technique sediment mineralogies can be used to calculate the relative flux of sediment from different tributaries thereby identifying sediment provenance

late holocene atmospheric dust deposition in eastern canada st lawrence north shore dust deposition in two ombrotrophic peatlands baie and ile du havre peatland idh bogs of the estuary and gulf of the st lawrence in eastern canada was reconstructed using elemental geochemistry the rare earth elements rees and other lithogenic element concentrations were measured by icp oes and q icp ms along two peat cores spanning the last 4000 years principal component analyses on the geochemical profiles show that rees display the same behavior as al ti sc and zr all conservative elements which suggests that rees are immobile in the studied peat bogs and can be used as tracers of dust deposition plant macrofossils were also used to infer past environmental and humidity changes the dust fluxes were reconstructed using the sum of rees ree the range of dust deposition varies from 0 2 to 3 8 g m 2 yr 1 in the baie bog while the idh bog shows lower fluxes ranging between 0 1 and 1 2 g m 2 yr 1 the highest dust fluxes in the baie bog were recorded from 1750 1000 cal bp to 600 100 cal

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

the loess cover of northeastern wisconsin abstract we present the first study of the distribution genesis and paleoenvironmental significance of late pleistocene loess in northeastern wisconsin and adjacent parts of michigan s upper peninsula loess here is commonly 25 70 cm thick upland areas that were deglaciated early and remained geomorphically stable preferentially accumulated loess by providing sites that were efficient at trapping and retaining eolian sediment data from 419 such sites indicate that the loess was mainly derived from proglacial outwash plains and to a lesser extent hummocky end moraines within and near the region particularly those toward the east of the loess deposits most of the loess was transported on katabatic winds coming off the ice sheet which entrained and transported both silt and fine sands the loess fines markedly and is better sorted distal to these source regions only minimal amounts of loess were deposited in this area via westerly winds this research 1 reinforces the observation that outwash plains and end moraines can be significant loess sources 2 provides evidence for katabatic winds as significant eolian transport vectors and 3 demonstrates that the loess record may be variously preserved across landscapes depending on where and when geomorphically stable sites became available for loess accumulation

a 37 000 year environmental magnetic record of aeolian dust deposition from burial lake arctic alaska abstract environmental magnetism and radiocarbon dating of burial lake sediments constrain the timing and magnitude of regional aeolian deposition for the noatak region of western arctic alaska for the last 37 000 years burial lake 68 43 n 159 17 w 21 5 m water depth is optimally located to monitor regional dust deposition because it is perched above local drainage and isolated from glacial processes cores collected in the summer of 2010 were studied through the application of magnetizations and progressive alternating field af demagnetization of u channel samples with additional data provided by computed tomography ct derived density hysteresis measurements isothermal remanent magnetization irm acquisition experiments organic carbon content biogenic silica physical grain size radiocarbon dating of wood seeds and plant macrofossils point source magnetic susceptibility and x ray fluorescence xrf with similar magnetic properties to regional alaskan loess deposits low coercivity highly magnetic material deposited during the late pleistocene contrasts with a high coercivity weakly magnetic component found throughout the record consistent with locally derived detritus the relative proportion of low coercivity to high coercivity magnetic material defined by the s ratios is used to reconstruct the regional input of dust to the basin over time a four fold decrease in the low coercivity component through the deglacial transition is interpreted to reflect diminished dust input to the region comparisons with potential sources of dust show that the timing of deposition in burial lake is largely consistent with general aridity lack of vegetative cover and increased windiness rather than glacial advances or retreats the influence from subaerial exposure of continental shelves cannot be ruled out as a significant far field source of dust to interior alaska during the last glacial maximum lgm but is unlikely to have been the sole source or to have contributed to increased dust in both the early and late holocene

revised 14 c dating of ice wedge growth in interior alaska usa to mis 2 reveals cold paleoclimate and carbon recycling in ancient permafrost terrain article i nfo establishing firm radiocarbon chronologies for quaternary permafrost sequences remains a challenge be cause of the persistence of old carbon in younger deposits to investigate carbon dynamics and establish ice wedge formation ages in interior alaska we dated a late pleistocene ice wedge formerly assigned to ma rine isotope stage mis 3 and host sediments near fairbanks alaska with 24 radiocarbon analyses on wood particulate organic carbon poc air bubble co2 and dissolved organic carbon doc our new co2 and doc ages are up to 11 170 yr younger than ice wedge poc ages indicating that poc is detrital in origin we con clude an ice wedge formation age between 28 and 22 cal ka bp during cold stadial conditions of mis 2 and solar insolation minimum possibly associated with heinrich event 2 or the last glacial maximum a doc age for an ice lens in a thaw unconformity above the ice wedge returned a maximum age of 21 470 200 cal yr bp our variable 14 c data indicate recycling of older carbon in ancient permafrost terrain resulting in radiocarbon ages significantly older than the period of ice wedge activity release of ancient carbon with climatic warming will therefore affect the global 14 c budget

sediment provenance of the wilderness barrier dunes southern cape coast south africa trace element geochemistry has been used to discern the provenance of sediments derived from geologically distinct sources found in a range of depositional settings this study investigates whether this approach can also identify provenance signatures in sediments derived from clastic sedimentary rocks of similar origins within a complex coastal transport environment the potential local sediment sources of a coastal barrier dune in south africa were analysed to assess their relationships with the barrier and whether these have varied with time results indicate that the oldest part of the barrier partly formed during mis 6 when sea levels were lower than at present has a closer affinity to fluvial sediment provided by local rivers than either younger samples from the barrier s seaward flank or the holocene dunes atop its crest both formed during sea level highstands constraints on the timing of barrier formation provided by osl dating proved helpful in discriminating between provenance and weathering signals terra nova 00 000 000 2010

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

implications of loess and fluvial deposits on paleoclimatic conditions during an icehouse hothouse transition capitanian upper quanzijie low order cycle bogda mountains nw china abstract permian terrestrial sedimentary records provide important clues on paleoclimatic conditions and changes in a vegetated planet during the last icehouse hothouse transition seven stratigraphic sections of middle permian upper quanzijie low order cycle qzj lc in bogda mountains nw china are studied to interpret the depositional environments and paleoclimatic conditions within a multi order stratigraphic framework the upper qzj lc contains distinct laterally persistent thick and massive red mudrocks interbedded with laterally discontinuous conglomerates the mudrocks are interpreted as loess deposits on the basis of their massive structure uniform multi modal grain size distribution lateral extent mineral composition and uniform detrital zircon ages thin conglomerates with a low relief erosional base are interpreted as ephemeral braided stream deposits whereas thick conglomerates with a high relief base that display a clear fining upward trend as meandering stream deposits in tarlong taodonggou area in the south common protosols in loess deposits indicate dust accumulation under arid to semiarid conditions in dalongkou 70 km to the north argillic protosols indicate subhumid conditions alternating with arid semiarid episodes gleysols in the upper part in both areas indicate a change to subhumid humid conditions at the end of qzj time the results strongly suggest that persistent aridity eolian processes and dust trapping mechanisms had existed in ne pangea during capitanian time the gradual but dramatic climatic change from arid semiarid to subhumid humid conditions at the end of capitanian correlates to and is the result of the global demise of the late paleozoic ice age

a loess paleosol record of climate and glacial history over the past two glacial interglacial cycles 150 ka southern jackson hole wyoming abstract loess accumulated on a bull lake outwash terrace of marine oxygen isotope stage 6 mis 6 age in southern jackson hole wyoming the 9 m section displays eight intervals of loess deposition loess 1 to loess 8 oldest each followed by soil development our age depth model is constrained by thermoluminescence meteoric 10 be accumulation in soils and cosmogenic 10 be surface exposure ages we use particle size geochemical mineral magnetic and clay mineralogical data to interpret loess sources and pedogenesis deposition of mis 6 loess was followed by a tripartite soil thin loess complex soils 8 7 and 6 apparently reflecting the large climatic oscillations of mis 5 soil 8 mis 5e shows the strongest development loess 5 accumulated during a glacial interval 76 69 ka mis 4 followed by soil development under conditions wetter and probably colder than present deposition of thick loess 3 43 51 ka mis 3 was followed by soil development comparable with that observed in soil 1 loess 1 mis 2 accumulated during the pinedale glaciation and was followed by development of soil 1 under a semiarid climate this record of alternating loess deposition and soil development is compatible with the history of yellowstone vegetation and the glacial flour record from the sierra nevada

making the material the formation of silt sized primary mineral particles for loess deposits abstract in 1911 e e free wrote it may be well to point out that there are really two problems of the loess a problem of the origin of material and a problem of deposition the problem of the origin of material has been relatively neglected in comparison to problems of deposition of the formation of deposits and latterly in comparison to studies of loess stratigraphy if we are to understand the true nature of loess this fascinating material we need to be aware of all the significant events in the processing of the particles which form a deposit a large amount of silt sized primary mineral material has to be produced to make a loess deposit loess is a quaternary phenomenon and we see the entire process being completed in quaternary times some powerful quaternary forces are able to produce very large amounts of granular material glacial grinding vigorously supported by smalley 1966a provides an obvious source for some loess material but the vast deposits of north china and central asia have no obvious glacial connection however they are adjacent to high asia a region of vast tectonic activity and an enormous release of terrestrial energy in the last several million years high asia is a large producer of loess silt much of which finds its way south to make the ganges delta but large amounts are moved north and east to make huge loess deposits africa presents a problem recent work e g coude gaussen 1987 suggests that there is a region of peri saharan loess but earlier observations e g penck indicate quite clearly that the sahara region is free of loess rathjens 1928 in his study of tripolitania indicated the presence of loess like deposits and described their nature but he did point out that 90 of the granular material was greater than 100 pm in diameter which would remove it from a strict loess definition on the soil taxonomy map of africa there is a belt of soil d3 which could include considerable loess deposits it stretches from the matmata loess in tunisia across northern libya to the western part of the egyptian coastal region if d3 contains loess this points to a genuine desert loess particle producing mechanism operating in the sahara

the geochemistry of loess asian and north american deposits compared abstract loess is widely distributed over asia and north america and constitutes one of the most important surficial deposits that serve as terrestrial records of the quaternary the oldest pleistocene loess in china is likely 2 6 ma thus spanning much or all of the pleistocene in north america most loess is no older than the penultimate glacial period with the exception of alaska where the record may go back to 3 0 ma on both continents loess deposits date primarily to glacial periods and interglacial or interstadial periods are represented by paleosols both glacial and non glacial sources of silts that comprise the bulk of loess deposits are found on both continents although loess has been considered to be representative of the average upper continental crust there are regionally distinctive compositions of loess in both asia and north america loess deposits in asia from yakutia tajikistan and china have compositionally distinct major element compositions due to varying abundances of silicate minerals carbonate minerals and clay minerals in north america loess in the mississippi river valley the great plains and alaska are also distinguishable with regard to major element composition that reflects highly diverse source sediments trace element geochemistry sc th zr and the rare earth elements also shows regional diversity of loess bodies in both asia and north america on both continents most loess bodies show significant contributions from later cycle altered sedimentary rocks as opposed to direct derivation from igneous rocks further some loess bodies have detectable contributions from mafic igneous rocks as well as major contributions from average upper crustal felsic rocks intercalated paleosols in loess sections show geochemical compositions that differ significantly from the underlying loess parent materials ratios of soluble to insoluble elements show depletions in paleosols due to chemical weathering losses of calcite dolomite plagioclase mica apatite and smectite in asia and north america the last interglacial paleosol is more weathered than equivalent modern soils which could be due either to a climate that was warmer and more humid a longer period of pedogenesis or both in asia early pleistocene loess and paleosols are both more weathered than those from the middle and late pleistocene forming prior to a mid pleistocene aridification of asia from uplift of the tibetan plateau understanding the geochemistry of loess and paleosols can tell us much about past atmospheric circulation past temperature and moisture regimes and even tectonic processes

geochemistry and mineralogy of the late pleistocene loess palaeosol sequence in zlota near sandomierz poland implications for weathering sedimentary recycling and provenance abstract in order to determine the provenance of material the late pleistocene loess palaeosol sequence in zlota poland was analysed geochemically icp ms icp es and mineralogically qemscan investigating simultaneously the weathering signature and effect of sedimentary sorting a total number of 39 loess and soil samples were tested for the geochemical composition and 5 for the mineralogy the investigated samples compared to upper continental crust are enriched with elements such as si zr hf nb ta th u and rare earth elements especially the heavy rare earth elements related rather to felsic igneous rocks the enrichment of only two mafic elements ti and cr can be explained by heavy minerals admixture loess in zlota is strongly mixed and homogenized during transportation and or sedimentary recycling for each sample the uniform shape of the chondrite normalized rare earth elements patterns were found characterized by steep light rare elements lan smn 3 45 4 08 avg 3 81 constant negative eu anomalies eu eu 0 50 0 63 avg 0 56 and distinctly flat heavy rare earth elements gdn ybn 1 17 1 45 avg 1 28 the material is not significantly affected by chemical weathering and the post depositional modifications are not particularly important for the trace element composition both in loess and soils e g th u 3 1 4 65 avg 3 64 ce ce 0 96 1 09 avg 1 01 lan ybn 6 22 7 93 avg 6 94 the research reveals that relatively fresh felsic related parent material has been well mixed during transportation but post depositional alterations related only to the pedogenesis have not been intense enough to mask their chemical signature the investigated material has been probably originated in scandinavia likely norway but deflated directly from the glacial drift covering the terrain of poland

structure of flow over alluvial bedforms an experiment on linking field and laboratory methods this paper presents results of a field study designed to examine the structure of flow over mobile and fixed bedforms in a natural stream and to compare the results with findings of previous laboratory studies within the framework of double time space averaging approach measurements of turbulence were obtained in a small river in illinois usa over a fine spatial grid of sampling points above a mobile sandy bedform and its artificially moulded replica flow structure over the artificial bedform is similar to that observed in laboratory studies but is markedly different from the flow structure over natural bedforms these differences are most pronounced in the roughness sublayer whereas flow in the logarithmic layer over natural and artificial sand waves is fairly similar and exhibits spatial uniformity the double time space averaged distributions of turbulence statistics conform to the multilayer model of flow structure over bedforms mean velocity distributions indicate neither classical flow recirculation nor substantial reduction of velocities in the lee of bedform crests however vertical patterns of turbulence statistics over depth suggest that stacked wakes similar to those observed in laboratory studies exist above the bedforms thus despite the absence of flow separation wake development seems to be induced by the systematic influence of upstream bedforms on the vertical structure of turbulence copyright 2006 john wiley sons ltd

geochemistry and mineralogy of late quaternary loess in the upper mississippi river valley usa provenance and correlation with laurentide ice sheet history abstract the midcontinent of north america contains some of the thickest and most extensive last glacial loess deposits in the world known as peoria loess peoria loess of the upper mississippi river valley region is thought to have had temporally varying glaciogenic sources resulting from inputs of sediment to the mississippi river from different lobes of the laurentide ice sheet here we explore a new method of determining loess provenance using k rb and k ba values in k feldspars and micas in loess from a number of different regions in north america results indicate that k rb and k ba values can distinguish loess originating from diverse geologic terrains in north america further different loess bodies that are known to have had the same source sediments using other criteria have similar k rb and k ba values we also studied three thick loess sections in the upper mississippi river valley region at each site the primary composition of the loess changed over the course of the last glacial period and k rb and k ba values parallel changes in carbonate mineral content and clay mineralogy we thus confirm conclusions of earlier investigators that loess composition changed as a result of the shifting dominance of different lobes of the laurentide ice sheet and the changing course of the mississippi river we conclude that k rb and k ba values are effective robust and rapid indicators of loess provenance that can be applied to many regions of the world

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

multi isotope approach δ44 40ca δ88 86sr and 87sr 86sr provides insights into rhizolith formation mechanisms in terrestrial sediments of nussloch germany abstract carbonates in loess paleosol sequences are considered as a valuable paleoenvironmental proxy for climate change during the quaternary period in this study we propose a new dataset of 44 40ca 88 86sr and 87sr 86sr to understand the formation of rhizoliths roots encrusted with caco3 within these kinds of sequences from nussloch region germany our results indicate that the leached fractions of rhizoliths sampled at 3 25 m 6 65 m and 8 45 m depths and leached with hcl have lower 44 40ca and 88 86sr and higher 87sr 86sr isotopic values than the leached fractions of rhizosphere and root free loess of the same stratigraphic levels this suggests different mechanisms of carbonate formation and different sources of sr and ca a three steps model of formation of rhizoliths from nussloch has been proposed first of all the roots grow in an existent stratigraphic level and the biological activity associated with roots allows for the dissolution of carbonate and non carbonate minerals a part of the available ca and sr is taken up by roots which absorb preferentially the light isotopes e g 40ca and 86sr a higher rate of water absorption by roots than nutrients in association with co2 released by biological respiration allows to reach supersaturation with respect to caco3 the precipitation of rhizolith carbonate selects preferentially the light isotopes e g 40ca and 86sr leading to lower 44 40ca and 88 86sr isotope values than the ones recorded on the closest rhizosphere and loess the higher 87sr 86sr signatures of rhizolith carbonates which is not modified by root uptake or by precipitation processes is the result of a mixture between 87sr 86sr signatures of carbonate and non carbonate minerals digested around the roots nevertheless grey zones remain in this main hypothesis about the very high contribution of residue materials to the isotopic signatures of rhizoliths in this light other mechanisms of downward transfer of ca and sr from upper stratigraphic level that could imprint the leached fractions of rhizoliths have been discussed

airborne dust transport to the eastern pacific ocean off southern california evidence from san clemente island 1 islands are natural dust traps and san clemente island california is a good example soils on marine terraces cut into miocene andesite on this island are clay rich vertisols or alfisols with vertic properties these soils are overlain by silt rich mantles 5 20 cm thick that contrast sharply with the underlying clay rich subsoils the silt mantles have a mineralogy that is distinct from the island bedrock silt mantles are rich in quartz which is rare in the island andesite the clay fraction of the silt mantles is dominated by mica also absent from local andesite and contrasts with the subsoils dominated by smectite ternary plots of immobile trace elements sc th la and ta nd cr show that the island andesite has a composition intermediate between average upper continental crust and average oceanic crust in contrast the silt and to a lesser extent clay fractions of the silt mantles have compositions closer to average upper continental crust the silt mantles have particle size distributions similar to loess and mojave desert dust but are coarser than long range transported asian dust we infer from these observations that the silt mantles are derived from airborne dust from the north american mainland probably river valleys in the coastal mountains of southern california and or the mojave desert although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin examination of satellite imagery shows that easterly santa ana winds carry abundant dust to the eastern pacific ocean and the california channel islands airborne dust from mainland north america may be an important component of the offshore sediment budget in the easternmost pacific ocean a finding of potential biogeochemical and climatic significance

distribution and composition of loess sediments in the ili basin central asia loess deposits in central asia provide an important record of regional climate and environmental change however in contrast to the intensively investigated loess deposits on the chinese loess plateau clp loess sediments in the ili basin of eastern central asia are poorly understood based on field investigation and existing literature this paper presents a preliminary study of the distribution strata and composition of the ili loess the distribution of the ili loess is clearly controlled by topographic and geomorphic conditions mainly in the river terraces low uplands and slopes of the tianshan mountains the thickness of the loess varies from several meters to over two hundred meters to characterize the ili loess composition the authors analyzed its grain size geochemistry x ray diffraction pattern and heavy mineral assemblage grain size analyses reveal that the ili loess consists predominantly of silt 4 63 mu m with a minor proportion of sand which is coarser than the loess of the clp and suggests a nearby provenance the bulk mineral components of the ili loess are dominated by quartz and feldspar with minor amounts of calcite chlorite mica dolomite and hornblende more than 20 types of heavy minerals were observed with major components of amphibole magnetite and epidote the major elements of the ili loess are characterized by high abundance of sio2 al2o3 and cao and minor amounts of fe2o3 mgo na2o and k2o compared to the clp loess the ili loess is relatively rich in na2o and displays higher na2o al2o3 ratios suggesting weak weathering the distribution patterns of rees indicate that both the ili loess and clp loess are of typical upper crustal composition with enrichment in lree negative eu anomalies and depletion of hree both the heavy mineral assemblage and geochemistry indicate that the local bedrock of the ili basin may have contributed only a little to the loess sediments c 2014 elsevier ltd and inqua all rights reserved

vertebrate tracks in pleistocene eolian sand sheet deposits of alaska abstract deformation structures interpreted as vertebrate hoof and foot tracks occur within upper pleistocene eolian sand sheet deposits in the stabilized kantishna sand sea of central alaska and in the nushagak lowland of southwestern alaska exposures of tracks are generally limited to cross sections which reveal concave up deformation structures in which displacement of preexisting strata diminishes downward deposits in both areas contain tracks that are 6 to 16 cm in diameter and are divided by a central ridge reflecting formation by artiodactyl even toed ungulates larger 21 34 cm tracks without a central ridge observed in the nushagak lowland were formed by proboscideans probably woolly mammoth large vertebrate tracks occur within irregularly stratified sand and silty sand that accumulated upon partially vegetated sand sheets and within thin even wind ripple laminae of unvegetated sand sheets the presence of tracks at multiple stratigraphic levels and preservation of roots and rhizocretions within the eolian deposits suggest that vegetated sand sheets may have formed a locally important grazing habitat for large herbivores during at least part of the last glaciation recognition that vertebrate tracks are preserved in eolian sand sheet deposits and in deposits of other environments as well opens a new source of stratigraphic and paleoecological data to aid reconstruction of the vanished ecosystems of beringia

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

geochemical characteristics of fine and coarse fractions of sediments in the yarlung zangbo river basin southern tibet china tracing sources of aeolian sediment is key to reconstructing earth surface processes in arid areas and interpreting the paleoenvironmental significance of aeolian sequences however the difference of geochemical characteristics between different fractions of sediments in the yarlung zangbo river basin yzrb is still unclear so we want to identify which fraction of sediments is more suitable for tracing sediment sources considering the long distance between different wide valleys in the yzrb we wonder whether there is any difference between these wide valleys in terms of geochemical characteristics of sediments forty three surface sediment samples in the yzrb are collected and the grain size distributions and the major element composition for 37 samples and the trace and rare earth element composition for the coarse 75 500 m and fine 75 m fractions of all samples are determined the results reveal the following 1 the fine fractions of the deposits contain more environmental information suggesting that the fine fractions cannot be directly compared between different climate zones for provenance identification and that appropriate coarse fractions based on the grain size distribution of the targeted sediments are more ideal for tracing sediment sources and 2 geochemical characteristics of various sediment types show spatial heterogeneity the coarse and fine fractions of the loose sediment samples can be divided into two regional groups based on geochemical characteristics the maquanhe zone in the upper reach the xigaze shannan and mainling zone in the middle reach which is consistent with the geological background of the yzrb 3 aeolian deposits in the yzrb are a local origin and predominantly derived from the adjacent loose sediments and fluvial sediments in the upper reach contribute little to the aeolian sands in the middle reach

geochemical composition of tajikistan loess and its provenance implications the tajikistan tj loess has great significance for the study of quaternary climate changes and dust source in central asia in this paper we investigate the geochemical composition and provenance of loess our results show that the major elements in order from high to low average content are sio2 al2o3 cao fe2o3 mgo k2o na2o tio2 p2o5 mno fe ti p and mn contents in loess are similar to those in the ucc as is the case with si al and mg contents in paleosols ca is distinctly enriched in loess and si al and k are depleted na is depleted in both loess and paleosols and p is depleted only in paleosols in contrast to the ucc paleosols show enrichments in all trace elements except for ba sr and zr but in loess some trace elements e g ba co ni and zr show depletion the cia value of tj loess is lower than that of kashmir loess the latter being influenced by differences in the sorting and tectonic environment there are no great changes about provenance during the formation of tj loess and the deposit areas have a shorter distance to the provenance geochemical data and atmospheric circulations demonstrate that the tj loess was mainly transported by the near surface northerly or northwesterly winds but there may be an additional and local source making a certain contribution to the formation of loess deposits in the south of tianshan

luminescence chronology of late pleistocene loess paleosol and tephra sequences near fairbanks alaska abstract thermoluminescence tl and infrared stimulated luminescence irsl sediment dating methods have been applied to paleosol and tephra bearing loess sequences younger than marine oxygen isotope stage mis 7 at three important sites tl ages indicate the development of significant paleosols 75 000 and 30 000 yr ago in the loess sequence at the gold hill site relatively minor soil development occurred 70 000 and 48 000 yr ago like the 75 000 yr old soil the 30 000 yr old soil is apparently of global extent and consistent in timing with inferred warm intervals elsewhere e g greenland europe western and central china at birch hill replicate tl dating of primary loess combined with two earlier tl results from the same site and with an earlier mean fission track glass shard age of 140 000 10 000 yr for the associated old crow tephra yield a more precise numeric age of 142 300 6600 yr for this alaska yukon chronostratigraphic marker ash bed three of the tl ages at the halfway house site are difficult to interpret but combined with other evidence they indicate 1 the upper 5 6 m of loess from halfway house is not part of the gold hill loess equivalent to pre mis 5 age as long thought by t l pewe but rather is much younger 2 the regionally significant variegated tephra found in the fairbanks and klondike areas and previously thought to be older than mis 5 has an age of 77 800 4100 yr late mis 5

discussion of geochemical evidence for the origin of late quaternary loess in central alaska in a recent paper muhs and budahn 2006 aim to test regional paleowind hypotheses put forth in the literature for the provenance of quaternary loess deposits in central alaska with geochemical evidence the experimental design of their study consists of a comparison and multilinear regression analysis mra of major element and rare earth element ree geochemistry between possible source sediment material along the yukon tanana and nenana rivers and the youngest loess units of three deposits near fairbanks alaska see their fig 2 such a study has been long overdue and we applaud their initiative however through this discussion letter we wish to address two points the first concerns the opposing hypotheses to be tested while the second concerns aspects of their experimental design muhs and budahn 2006 pp 324 325 set out to test the opposing hypotheses of northerly versus southerly paleowinds for the origin of quaternary loess in central alaska literature accounts of paleowind reconstructions are either based on sand dune orientations and sand sheet locations or loess deposits for both types of archives sand and loess the inferred paleowinds are presented by the authors as inconsistent and contradictory we argue that the platform on which this paper is set up i e north versus south is built from a misinterpretation and inaccurate representations of previous work referenced as supporting evidence furthermore temporal variability an important issue appears to be cast aside concerning aeolian sand deposits in the inner parts of central alaska hopkins 1982 and lea and waythomas 1990 conclude winds came from a northeasterly direction during the last glacial maximum muhs and budahn 2006 hypothesize p 324 from the occurrence of aeolian sands of early holocene age north of9the yukon river near the confluence of the porcupine river see froese et al 2005 and their fig 1 for location that winds must

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

transatlantic distribution of the alaskan white river ash volcanic ash layers preserved within the geologic record represent precise time markers that correlate disparate depositional environments and enable the investigation of synchronous and or asynchronous behaviors in earth system and archaeological sciences however it is generally assumed that only exceptionally powerful events such as supereruptions 450 km3 of ejecta as dense rock equivalent recurrence interval of 105 yr distribute ash broadly enough to have an impact on human society or allow us to address geologic climatic and cultural questions on an intercontinental scale here we use geochemical age and morphological evidence to show that the alaskan white river ash eastern lobe a d 833 850 correlates to the ad860b ash a d 846 848 found in greenland and northern europe these occurrences represent the distribution of an ash over 7000 km linking marine terrestrial and ice core records our results indicate that tephra from more moderate size eruptions with recurrence intervals of 100 yr can have substantially greater distributions than previously thought with direct implications for volcanic dispersal studies correlation of widely distributed proxy records and volcanic hazard assessment

on the origins of mesospheric gravity waves 1 using hourly data from a three year simulation based on a gravity wave resolving general circulation model we have first inferred a global view of gravity wave sources and propagation affecting significantly the momentum balance in the mesosphere the meridional cross section of momentum fluxes suggests that there are a few dominant propagation paths originating from the subtropics in summer and the middle to high latitudes in winter these gravity waves are focused into the mesospheric jets in their respective seasons acting effectively to decelerate the jets the difference in the source latitudes likely contributes to the hemispheric asymmetries of the jets the horizontal distribution of the momentum fluxes indicates that the dominant sources are steep mountains and tropospheric westerly jets in winter and vigorous monsoon convection in summer the monsoon regions are the most important window to the middle atmosphere in summer because of the easterlies associated with the monsoon circulation

paleowind directions from the magnetic fabric of loess profiles in central alaska abstract two parallel profiles of alternating loess and paleosol horizons from the halfway house site west of fairbanks in central alaska were evaluated in terms of their potential for preserving paleowind directions combined the profiles span specmap marine oxygen isotope stages 1 6 approximately the last 150 ka our analytical tools consisted of measuring the sample s anisotropy of magnetic susceptibility and characterizing the magnetic mineralogy by multiple approaches both primary eolian and secondary reworked magnetic fabrics are recognized along certain intervals of both profiles primary eolian fabrics display a horizontal magnetic foliation and a well defined magnetic lineation corresponding to the paleodirection of sediment transport and deposition a systematic change in transport direction is observed where long term prevailing winds appear to shift from a nw se to n s direction during glacial and interglacial periods respectively

150 000 years of loess accumulation in central alaska abstract the halfway house site in interior alaska is arguably the most studied loess deposit in northwestern north america the site contains a complex paleomagnetic and paleoenvironmental record but has lacked the robust chronologic control that would allow its full potential to be exploited detailed reexamination of stratigraphy paleomagnetics and tephrostratigraphy reveals a relatively complete marine isotope stage mis 6 to holocene record constrained by the old crow 124 10 ka vt 106 10 ka sheep creek klondike ca 80 ka dominion creek 77 8 ka and dawson ca 30 2 cal ka bp tephras we show two well developed paleosols formed during marine isotope stages mis 5e and 5a while mis 5c and 5b are either poorly represented or absent the new tephrostratigraphy presented here is the most complete one to date for the late pleistocene and indicates mis 5 sediments are more common than previously recognized a magnetic excursion within the sediments is identified as the post blake excursion 94 1 7 8 ka providing independent age control and adding to the increasing body of evidence that alaskan loess is a detailed recorder of variations of the earth s magnetic field over time a high resolution magnetic susceptibility profile placed into this new chronostratigraphic framework supports the hypothesis that wind intensity is the main variable controlling fluctuations in susceptibility correlation of the susceptibility record to global marine 18o records is complicated by highly variable accumulation rates we find the lowest rates of accumulation during peak warm and cold stages while abrupt increases are associated with periods of transition between marine isotope sub stages building on previous accumulation models for alaska surface roughness is likely a leading variable controlling loess accumulation rates during transitions and peak cold periods but the negligible accumulation during mis 5e and 5a suggests that loess production was exceedingly low negating the role of surface roughness this interplay of variables leads to optimal conditions for loess accumulation during transitions between isotope stages and to a somewhat lesser extent stadials and interstadials

holocene proglacial loess in the ranwu valley southeastern tibet and its paleoclimatic implications abstract glaciers and aeolian sediments are widespread on the tibetan plateau although glaciations have played an important role in the formation of loess in many glaciated regions in the northern hemisphere proglacial loess on the tibetan plateau is rarely reported and its origin source and paleoclimatic implications remain unclear we have found a small area of proglacial loess deposits in the ranwu valley southeastern tibet grain size geochemical and geomorphologic evidence as well as observations of local dust storms reveal that the outwash sediments of the laigu glacier 30 km long are the primary source for the local loess we also found that the glacial wind from this glacier is the main transport vector and thus speculate that the onset of the ranwu loess at ca 6 6 ka correlates with the early neoglacial advance of the laigu glacier which generated glacial winds and local dust storms in the closed and deep incised glacial valley this is supported by the basal radiocarbon ages of two ice cores and a synthesis of holocene glacial stadials on the tibetan plateau loess layers and paleoclimatic proxies indicate two drought stages at ca 6 6 6 ka and ca 2 9 ka to the present corresponding to two well documented weakened stages of the indian summer monsoon this study highlights that although local aeolian sediments always cover a small area they also have potential to record some clues of regional climate changes in some alpine regions much more detailed studies should be done to reveal their specific formation mechanisms and paleoclimatic implications

origin of last glacial loess in the western yukon tanana upland central alaska usa loess is widespread over alaska and its accumulation has traditionally been associated with glacial periods surprisingly loess deposits securely dated to the last glacial period are rare in alaska and paleowind reconstructions for this time period are limited to inferences from dune orientations we report a rare occurrence of loess deposits dating to the last glacial period 19 ka to 12 ka in the yukon tanana upland loess in this area is very coarse grained abundant coarse silt with decreases in particle size moving south of the yukon river implying that the drainage basin of this river was the main source geochemical data show however that the tanana river valley to the south is also a likely distal source the occurrence of last glacial loess with sources to both the south and north is explained by both regional synoptic scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the brooks range to the north and the alaska range to the south based on a comparison with recent climate modeling for the last glacial period seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources

reply to the discussion by f lagroix and s k banerjee of geochemical evidence for the origin of late quaternary loess in central alaska we thank f lagroix and s k banerjee 2006 for their interest in our recent paper and welcome this opportunity to clarify our thoughts on the issues they raise lagroix and banerjee 2006 state that we have misinterpreted past work on paleowinds of alaska and furthermore that considerations of temporal variability have been cast aside we believe that lagroix and banerjee 2006 have misinterpreted our statements about last glacial paleowinds versus early holocene winds in the yukon river valley we stated that hopkins 1982 and lea and waythomas 1990 presented a picture of northeasterly winds to explain eolian sand distribution over much of alaska during the last glacial period we then cited the yukon river example of froese et al 2005 holocene eolian sands on the north side of the river as an example of how paleowinds may have changed at the end of the last glacial period we stated the following muhs and budahn 2006 p 324 if the ages are maximum limiting estimates and if the sands were locally derived these deposits imply sand transporting winds from the south by the start of the holocene italics added for emphasis this statement coming after our summary of northeasterly paleowinds from hopkins 1982 and lea and waythomas 1990 was intended to show not a contradiction but a shift in winds from glacial to interglacial time furthermore we do not disagree with lagroix and banerjee 2006 that the deposits studied by froese et al 2005 could have come from the north derived from the porcupine river we qualified our statement about both the age and the source of the sands with the word if which emphasizes the uncertainty we had at that time and still have today until provenance studies are conducted the source or sources of eolian sand along the yukon river are purely speculative

late pliocene dawson cut forest bed and new tephrochronological findings in the gold hill loess east central alaska thick loess deposits in the fairbanks region of interior alaska are a rich source of information on past climates and environments during the late cenozoic and the numerous distal silicic tephra beds preserved within them offer the potential for good chronological control the dawson cut forest bed lies in the lower part of this loess cover plant macrofossils consist of picea glauca picea mariana betula papyrifera and populus balsamifera but no pinus these fossils together with the abundance and size of spruce remains pollen tree ring characteristics and 13 c values of spruce wood demonstrate that the boreal forest represented by the dawson cut forest bed was similar to the modern boreal forest of central alaska warming conditions during the early part of the dawson cut interglaciation initiated thawing of permafrost and melting of ground ice as evidenced in the presence of ice wedge casts and major erosion of the lower gold hill loess tephrochronological magnetostratigraphic and glass fission track dating studies in the fairbanks area and at the palisades site on the yukon river in central alaska suggest an age for the dawson cut forest bed of ca 2 ma hence the northern boreal forest of northwestern north america as we know it today has a long history that probably extends back to at least 2 ma

the role of african dust in the formation of quaternary soils on mallorca spain and implications for the genesis of red mediterranean soils abstract african dust additions explain the origin of terra rossa soils that are common on the carbonate platform island of mallorca spain mineralogical and geochemical analyses indicate that quaternary carbonate eolianites on mallorca have a very high purity usually composed of more than 90 carbonate minerals calcite dolomite and aragonite in contrast terra rossa soils developed on these eolianites have lower carbonate contents and contain higher concentrations of quartz and other silicates analyses of immobile trace elements indicate that the non carbonate fractions of the eolianites have distinctive zr hf la yb cr sc and th ta values that differ from the superjacent terra rossa soils these observations indicate that even if sufficient dissolution of the eolianite had taken place to create the soils by residual accumulation immobile element ratios in the soils require an external source however zr hf la yb cr sc and th ta values in the soils fall within the range of values for these element ratios in african dust collected on barbados and mainland spain we conclude that the silicate fractions of terra rossa soils on mallorca are derived mainly though not wholly from far traveled african dust and this process may explain the origin of other terra rossa soils found in southern europe

constraining spatial variability of methane ebullition seeps in thermokarst lakes using point process models 1 ebullition is an important but highly heterogeneous mode of methane emission in lakes variability in both spatial distribution and temporal flux creates difficulty in constraining uncertainties in whole lake emission estimates analysis of short and long term flux measurements on 162 ebullition seeps in 24 panarctic lakes confirmed that seep classes identified a priori according to bubble patterns in winter lake ice have distinct associated fluxes irrespective of lake or region to understand the drivers of ebullition s spatial variability and uncover ways to better quantify ebullition in field work we combined point process modeling with field measurements of 2679 gps marked and classified ebullition seeps in three alaskan thermokarst thaw lakes that varied by region permafrost type and seep distribution spatial analysis of field data revealed that seeps cluster above thawed permafrost soil mounds in lake bottoms seep density and clustering determined from field observations were used as parameters in a poisson cluster process model to simulate seeps across entire lake surfaces sampling results indicated that 1 applying seep class mean flux values to unmeasured seeps counted on ice bubble surveys does not compromise accuracy of whole lake flux estimates 2 three distributed 50 m2 ice bubble survey transects more accurately estimate mean lake ebullition than 17 dispersed 0 2 m2 bubble traps and 3 the uncertainty associated with whole lake mean ebullition estimated by lake ice survey transects is inversely related to seep density findings suggest that transect field data collected on a large number of widely distributed lakes can be combined to provide a well constrained bottom up estimate of regional lake ebullition

cryptic post depositional reworking in aeolian sediments revealed by the anisotropy of magnetic susceptibility abstract our anisotropy of magnetic susceptibility ams investigation of the gold hill steps ghs2 and halfway house hh3 loess and paleosol profiles in central alaska confirms that post depositional reworking of loess at gold hill steps has taken place and of greater importance identifies the reworked depth intervals in ghs2 the majority of the loess below 7 80 m depth has been reworked the loess at the halfway house site is as stated in the literature a predominantly undisturbed aeolian deposit however we have identified two intervals that have been reworked in hh3 we infer from the depth variation of the ams orientation distribution at ghs2 that the presence of permafrost in the past was the dominant active mechanism producing the observed deformations permafrost loess behaved 1 as impermeable layers focusing and channeling flow most likely that of groundwater and 2 as rigid bodies undergoing rotations and lateral translations a modern analogue of focused flow by an impermeable layer is identified at hh3

geochemical evidence for provenance diversity of loess in southern china and its implications for glacial aridification of the northern subtropical region abstract the thick xiashu loess in southern china is distributed not only in the yangtze river valley but also and most extensively in the region between the qinling mountains and the lower reaches of the yangtze river however there are few studies of the provenance and climatic implications of the xiashu loess in this latter region here we present the results of a provenance study of last glacial loess samples from twenty two typical xiashu loess sections using the major and trace element composition as a provenance indicator seventeen of the sites are located to the north of the yangtze river and our primary aim was to determine the provenance of the xiashu loess within this region our results indicate that the alluvial plain located mainly in the present drainage area of the huai river was the primary dust source for the xiashu loess in this region the occurrence of multiple local dust sources within this alluvial plain suggested by their geochemical heterogeneity indicates that the alluvial plain experienced intensified aridity which caused it to become a dust source for local loess deposits in northern subtropical china during the last glacial our study provides strong evidence to challenge the long held view that the occurrence of xiashu loess resulted from the southward incursion of the clp loess deposits sourced from deserts of the asian interior and it confirms the substantial role of aridification of the present humid northern subtropical region for dust emission to the climate system during the last glacial

geochemistry of a late quaternary loess paleosol sequence in central argentina implications for weathering sedimentary recycling and provenance abstract a loess paleosol sequence in the pampean plain central argentina was analyzed geochemically in order to evaluate the weathering signature and sedimentary recycling as well as to analyze the origin of these loessic sediments corralito i sequence is composed of three paleosols and a buried soil separated by loess layers the loess paleosol sequence shows a similar geochemical composition throughout suggesting that pedogenesis has not been intense enough to mask the chemical signature of the parent material weathering indices cia ciw pia and lwi elemental ratios rb sr cao tio2 and na2o tio2 and the a cn k ternary diagram indicate incipient chemical alteration for this sequence compatible with a weathering limited regime as expected paleosols cias 60 exhibit a slightly higher chemical alteration than loess layers cias 58 mass balance calculations reveal the losses of some major oxides i e cao na2o and sr in the buried soil and paleosols compared to its loess mantles reflecting the weathering of plagioclase besides the losses of k2o and ba in the buried soil and paleosols i and ii when compared to its loess layers suggest the chemical alteration of k feldspar the chemical alteration of volcanic glass is evidenced by the relative losses of as in almost all levels conversely the relative gains of fe2o3 and mgo reveal that pyroxenes and amphiboles or fe oxy hydroxides are concentrated in paleosols and the buried soil compared to its loess mantles the geochemical approach used to constrain the origin of these pampean plain loessic sediments indicates they derive mainly from the andean region conversely the pampean ranges the parana river basin and uruguayan precambrian outcrops which were pointed out as minor local sources do not contribute significantly to the loess deposits this work also shows that corralito i loess paleosol sequence and other loess samples from argentina do not evidence sedimentary recycling suggesting that these pampean plain loess deposits are mainly composed by young materials derived from undifferentiated volcanic rocks

stratigraphy geochemistry and thermoluminescence ages of lower mississippi valley loess four periods of loess deposition in the lower mississippi valley can be identified on the basis of geochemical and mineralogical criteria radiocarbon dating and thermoluminescence dating these are designated loess units 1 2 3 and 4 in order of increasing age carbonate rich unit 1 loess comprises more than 70 per cent of the thickness of the loess profiles 14c and tl dates indicate this loess was deposited between 9 000 and 20 000 years ago a maximum sedimentation rate of 2 17 mm yr 1 has been recorded near vicksburg just after the last laurentide glacial maximum between 17 190 and 15 580 years ago the unit 2 loess which is thin and partly decalcified was deposited slowly between about 25 000 and 20 000 years ago the unit 3 and unit 4 loess formations which are both highly weathered have yielded tl ages of 76 000 85 000 years and 119 000 132 000 years suggesting they were deposited during the altonian substage of the early wisconsinan and the illinoian glacial stage respectively the four loess units are stratigraphically equivalent to the peoria farmdale roxana and loveland loess formations previously recognized in illinois the source of dust in both areas was glacial outwash in the mississippi valley during interglacials and interstadials when the supply of glacial debris was reduced and the mississippi river changed from a braided to a meandering regime dust sedimentation in southern mississippi virtually ceased allowing weathering and pedogenesis to proceed

using pca to characterize and differentiate loess deposits in wisconsin and upper michigan usa abstract data on loess thickness as well as a variety of particle size fractions were determined for 875 samples taken from several loess sheets across wisconsin and upper michigan because the particle size characteristics of these samples varied widely within and between the loess sheets we used principal components analysis pca as a way of isolating the major textural components or signals that exist across the various loess sheets the purpose of this research was to examine and interpret these principal components or particle size signatures common to the different loesses in order to better understand the loess sheets character formation mechanisms and likely sources our initial assumption that many of these loesses varied markedly from the classical silty loess was supported by the particle size data and the pca although component 1 was interpreted as thick silty loess dominated by medium silts component 2 was mainly composed of very fine sand and coarse silt and is better viewed as coarse loess components 3 and 4 were less texturally homogeneous and may reflect mixing between the loess and the underlying sediment especially where the loess is