chronology of late wisconsinan glaciation in middle north america abstract we propose a chronology of late wisconsinan glacial fluctuations in middle north america from alberta to wisconsin based on radiocarbon dates derived solely from wood previous chronologies of the southwestern margin of the north american continental ice sheet have depended to a considerable degree on radiocarbon dates from fine grained organic sediment this material is commonly contaminated with older carbon resulting in chronologic confusion by using only dates from wood much of the confusion disappears however because of the scarcity of wood dates only four of the sixteen identified fluctuations are accurately dated an advance into iowa about 14 000 to 13 500 bp an advance into south dakota and iowa about 12 300 bp an advance into the lake michigan basin about 11 700 bp and an advance into the lake superior basin about 9900 bp in addition the beginning of late wisconsinan glaciation before 20 000 bp is fairly well documented none of the fluctuations in the western part of the region are accurately dated

application of osl single aliquot and single grain dating to quartz from anthropogenic soil profiles in the se united states abstract reduced luminescence intensity in soils is a widespread phenomenon but is not understood we examine the distributions of equivalent dose d e values of quartz from surface and buried soils from earthen mounds in louisiana where pedoturbation is the likely cause of luminescence resetting we first investigated the effectiveness of optical bleaching in surface samples similar in composition and environment to those at depth resulting d e distributions from the top 10 cm of the topsoils approach 0 gy the concentration of zero age grains decreases rapidly with depth paleosol ages based on low values of the d e distribution demonstrate good agreement with previously published ages we propose a three zone model for the explanation of surface bleaching in which the soil surface is continuously stressed and loaded by subsurface turbation mechanisms creating surface relief surface relief is reduced by subaerial impact and transport forces causing disaggregation and single grain dispersion this results in a surface bleaching zone where soil particles and topography are in constant transition suggesting that many soils may offer frequent and thorough presentation of mineral grains to surface insolation and thus high concentrations of zero dose grains

tracking textural mineralogical and geochemical signatures in soils developed from basalt derived materials covered with loess sediments sw poland abstract this study investigates the scale of inheritance of signatures typical of loess and basalt derived substrates in soils having both components present as parent material due to past periglacial processes based on field description particle size distribution mineralogy heavy minerals and clay minerals as well as geochemistry we track the signal of both materials local basalt derived and loess derived estimate the maximum thickness of loess mantles and mixed zones having both loess and basaltic components and note the presence or absence of basal layers without allochtonous additions the results show that geochemistry and heavy minerals are the most reliable proxies for a verification of aeolian silt contributions and to define individual layers in complex soil parent materials soil formation in the studied landscape depends on the type of slope sediments typical fine grained weathering of basalt without input from aeolian silt would promote rather vertic development however in thick loess deposits as well as in thin silt textured materials superimposed on clay loam beds clay illuviation dominates development of argic horizons however results in decreasing permeability promoting water stagnation and enhanced degradation processes in clay rich subsoil instead of luvisols stagnosols and retisols developed in the study regions basaltic block covers mixed with loess host cambic horizons based on our findings it seems that at the edge of thin loess deposits no soils exist that developed exclusively from basaltic parent materials

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

osl ages and possible bioturbation signals at the upper paleolithic site of lagoa do bordoal algarve portugal abstract three sediment samples were collected from a soil profile at the lagoa do bordoal site algarve portugal quartz extracted from soil horizons within the profile was optically dated using the single aliquot regenerative dose sar protocol outlined by murray and wintle radiation measurements 5 2000 523 the optically stimulated luminescence osl emitted by quartz within the 90 150 m size range was measured using three aliquot sizes the equivalent doses d e that were obtained show an asymmetric distribution as the numbers of grains in each aliquot are reduced the distribution of doses is clearly shifted to lower d e values including zero doses on single grain aliquots this shift is accompanied by an increase in the asymmetry of the distribution these patterns indicate that as the aliquot size decreases the distributions are increasingly characterized by aliquots with lower d e s with respect to the present day modern surface this shift is most evident in the sample collected from a depth of 37 cm within an ancient b horizon it is least evident in the sample located only 10 cm below it within a sand unit an asymmetric distribution of d e s can be a result of a large number of grains that were well bleached at burial being mixed with a small number of grains that were partially bleached at that time radiation measurements 30 1999 207 however the shift in d e s that is seen in the lagoa east samples is most likely due to the postburial downward movement of fully and partially bleached grains from the surface with possible contributions from the downward movement of grains that received low doses while buried in overlying horizons the simplest explanation for our results is that grains carrying zero or small d e s have been moved downward during bioturbation events these results suggest that downward bioturbation in ancient soil profiles can be identified based on the osl characteristics of quartz grains we are also able to provide a minimum age of 24 4 3 2 ka for the upper palaeolithic lithic assemblage at the site

evaluation of parent material uniformity criteria in loess influenced soils of west central kentucky abstract parent material relations in loess influenced soils of west central kentucky were studied to better understand the nature of the loess and its impact on the soils of that area twenty one stable landscape positions were sampled on two adjoining transects trending northwest to southeast from the ohio river to the tennessee border profiles were described in the field and samples were collected for particle size mineralogical and other laboratory analyses the soils consisted of a variable thickness loess mantle overlying residuum derived materials weathered from sandstone siltstone shale and limestone diffuse lithologic discontinuities indicating a gradual change from loessial to residual materials were observed in both field and laboratory data in most cases the laboratory data supported the presence and position of lithologic discontinuities identified by field morphology loessial and residual materials were best differentiated by clay free particle size distribution and k 2 o in the coarse silt fraction soil derived from loess and residuum was mixed at the interface of those materials the mixing was more intense where loess was thin a simple index was used to identify relative influence from each parent material type in the mixed zones

soil forming intervals caused by eolian sediment pulses in the lahontan basin northwestern nevada we have studied a series of toyeh post isotope stage 2 eolian dust fall was the source of fines and salts in these soils apparently this influx was concentrated during two brief intervals or pulses one during the holocene and one during the previous isotope stage 5 interpluvial leaching during the sehoo pluvial removed salts from churchill soils carbonate and soluble salts now observed in the churchill soils represent a toyeh overprint on the churchill profile these pulses of fine sediment and accompanying salts are tantamount to the soil forming intervals that morrison described in the lahontan area episodic eolian dustfall provides fine particles of silicates calcite and soluble salts that infiltrate into the clast supported alluvial piedmont sediments several hundred playas exist in the basin and range each providing directional dust contributions that influence local and regional soil development we counsel caution in assuming constant gradual development of soil properties without due consideration of paleoenvironmental influences on soil forming factors

application of transient electromagnetic and audio magnetotelluric methods for imaging the monte real aquifer in portugal fifty transient electromagnetic tem and 15 audio magnetotelluric amt soundings were carried out in the west central part of portugal over an area of approximately 40 km2 to characterize the geological formations associated with the monte real aquifer in order to 1 assess the spatial extent of the aquifer 2 detect the zones of higher water productivity and 3 evaluate the aquifer salinization risk the dimensionality and strike direction of the amt profiles were studied using phase tensor analysis and the amt data was inverted using a two dimensional 2d nonlinear conjugate gradient algorithm in addition the tem soundings were inverted using a one dimensional 1d levenberg marquardt technique in order to obtain 1d layered earth resistivity models the tem results reveal that the aquifer is not uniform in the study area a more resistive zone is evident in the north and northeast of the investigated area where we expect to have higher productivity on the other hand the amt models suggest that the aquifer basement is probably located at a depth of more than 800 m based on the results of this investigation no traces of saltwater intrusion were found for the monte real aquifer therefore we assume that the risk of saltwater intrusion is small in the study area

high resolution chronologies for loess comparing ams 14c and optical dating results the nuxloch loess section in south west germany is famous in central europe for its thick deposits from the last glacial maximum it has therefore been intensively studied during the past few years and offers an excellent opportunity to compare the performance of different dating techniques covering the period 15 45 ka here we present results fromoptical and ams 14 c dating the silt sized polymineral fraction of the clastic sediments and a multiple aliquot approach was used for ir osl dating 14 c dating was carried out on organic macro remnants and humin fractions extracted fromthe sedim ents with the exception of samples taken from the uppermost 1 5 m of the section ir osl and calibrated 14 c ams ages are consistent over the entire period the inconsistencies in the upper meters are thought to be due to disturbances during soil formation in the holocene the good agreement obtained on the remaining sequence demonstrates the high accuracy of both methods when studying loess sections for the ir osl ages no significant age underestimations are obvious the results clearly document that accurate chronologies can be developed for such continental sedimentary sequences this gives access to archives that can now be studied with a high temporal resolution and allows the establishment of new paleoclimatic proxies for the study of terrestrial responses to past climatic changes r 2003 elsevier science ltd all rights reserved

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

coarse textured basal zones in thin loess deposits products of sediment mixing and or paleoenvironmental change abstract the purpose of this research was to characterize and interpret the coarse basal zones that are common in thin loess deposits that overlie coarser textured sediment to that end we sampled nine pedons in northeastern wisconsin and the upper peninsula of michigan each of which had formed in thin 55 cm loess over sandy glacial sediment at most of these sites the loess became noticeably coarser near the lithologic discontinuity the loess has a primary particle size mode in the coarse silt or fine very fine sand fraction 30 65 m and a secondary mode in the fine or medium sand fraction 200 400 m we attribute the secondary mode to mixing of underlying sands into the loess either during loess deposition or by post depositional pedoturbation in thin loess pedoturbation processes can penetrate into the underlying sediment facilitating mixing upward as far as 50 cm into the loess silt from the loess has also been mixed into the underlying sandy sediment alternatively in some pedons the loess itself coarsens with depth the particle size mode for the loess becomes increasingly coarser with depth this coarsening suggests that during loess deposition one or more of the following was occurring 1 wind velocities were decreasing over time 2 the textural character of the loess source area s were changing decreasing or 3 additional source areas with finer textured sediment became more dominant over time our research demonstrates the utility of detailed particle size data for detecting and interpreting the paleoenvironmental history of loess we also document the extent to which pedoturbation can impact the original textural characteristics of loess or any sediment that occurs as a thin surficial mantle

mid wisconsinan stratigraphy and paleoenvironments at the st charles site in south central iowa a sequence of loess mantled sediments exposed along clanton creek provides the first evidence of fluvial pedologic and biotic environments before the last glacial maximum in south central iowa two fining upward fluvial sequences one inset into the other are exposed radiocarbon ages indicate that the alluvial fills are about 34 000 yr old basal gravel in the oldest fill contains well preserved mammoth mammuthus bones sparse seeds from this horizon suggest weedy flood plain conditions the younger alluvial fill contains well preserved pollen plant macrofossils and insects the pollen is dominated by nonarboreal taxa and pinus suggesting a prairie border or savanna environment vascular plant and bryophyte macofossils indicate a variety of aquatic and marsh environments on the flood plain insects are mostly sympatric in mixed conifer and hardwood forest that extends along latitude 47 to 49 between eastern north dakota and new england but forest beetles are rare and the fauna is dominated by openground forms the site is interpreted as an open flood plain dotted with marshes and oxbow lakes it was surrounded by open woodland or savanna similar to that in north eastern north dakota at present july temperatures at the st charles site were probably 3 to 5 c cooler than those at present the pre loess stratigraphy of the site differs markedly from that of upland sites and demonstrates that correlation between upland and lowland sequences cannot be done without adequate dating

recognition and characterisation of the aeolian component in soils in the girilambone region north western new south wales australia abstract characterisation of aeolian material in the girilambone region of new south wales 600 km nw of sydney using particle size analysis mineralogy geochemistry and micromorphological analysis shows that it consists of spheroidal highly abraded 70 m quartz grains although relatively pure aeolian accessions are found on top of tertiary leucitite flows the aeolian material is generally admixed with residual and transported soil to a depth of 0 3 m throughout the region this study has established a set of criteria for identifying the aeolian contribution to soils in the girilambone region of north western new south wales where it is difficult to distinguish these include a characteristic particle size of 70 m of the quartz grains highly abraded and spherical morphology presence of thin clay coats on well rounded grains and gradational patterns in particle size distribution mineralogy and geochemistry through the soil profile these types of soils with a high content of silt and fine sand do not readily form aggregates particularly where they have low organic content to improve the sustainability of cropping and pastoral activities on these soils their management should aim to maintain or increase structural stability for example by addition of organic material mineral exploration procedures should avoid the diluting aeolian component by sampling the 150 m fraction from surficial soils or material from below 0 3 m

characterisation of two fluvio lacustrine loessoid deposits on the island of gran canaria canary islands abstract the canary islands are close to the largest desert in the world the sahara and as a result the influence of air transported dust in the area is of great significance the present analysis consists of a study of two deposits in the ne and nw respectively of the island of gran canaria considered as fluvio lacustrine loessoids they exhibit the characteristics of aeolian deposits re worked by fluvial processes at the mouth of gullies and later edaphized in the nw profile galdar formed from 400 ka to present there are four different levels with abundant manganese stains over each and separated by dense calcrete laminations this sequence may be associated with cyclical processes of deposits in humid conditions and drying mn mobility plus the formation of arid soil carbonate precipitation the formation of the galdar profile took place between the upper pliocene and the upper pleistocene holocene the ne profile jinamar reveals a similar cyclic profile the jinamar fluvio loess deposit was formed between the upper pliocene and the upper pleistocene 1 96 0 1 ma the high percentage of the silt fraction 60 90 and the high percentage of quartz a mineral which is totally imported from the sahara desert are the main arguments in favour of the definition of these loess like deposits

eolian sand and loess deposits indicate west northwest paleowinds during the late pleistocene in western wisconsin usa our study adds to the quaternary history of eolian systems and deposits in western wisconsin usa primarily within the lower chippewa river valley thickness and textural patterns of loess deposits in the region indicate transport by west northwesterly and westerly winds loess is thickest and coarsest on the southeastern flanks of large bedrock ridges and uplands similar in some ways to shadow dunes in many areas sand was transported up and onto the western flanks of bedrock ridges as sand ramps presumably as loess was deposited in their lee long linear dunes common on the sandy lowlands of the chippewa valley also trend to the east southeast small depressional blowouts are widespread here as well and often lie immediately upwind of small parabolic dunes finally in areas where sediment was being exposed by erosion along cutbanks of the chippewa river sand appears to have been transported up and onto the terrace treads forming cliff top dunes luminescence data indicate that this activity has continued throughout the latest pleistocene and into the mid holocene together these landforms and sediments paint a picture of a locally destabilized landscape with widespread eolian activity throughout much of the postglacial period

age verification of the lake gribben forest bed and the younger dryas advance of the laurentide ice sheet analysis of nine wood samples from the lake gribben forest bed near lake gribben michigan yielded a combined age of 10 025 100 14c years bp which confirms and refines prior age estimates for the bed the stratigraphic position of these samples below a prograding ice contact fan indicates the time that a glacial margin reached the southern edge of the lake superior basin geomorphic tracing and correlation of associated deposits indicate that a contemporaneous margin extended almost 1000 km from duluth minnesota across the lake superior basin to north bay ontario along the southern shore of lake superior ice margin expansion began during and ended at the close of the younger dryas a surging glacier system would not produce a nearly linear moraine system across both a major basin lake superior and a major upland abitibi upland therefore we attribute this advance of the laurentide ice sheet to climatic forcing of the younger dryas event

chemical and particle size evidence for addition of fine dust to soils of the midwestern united states significant long term atmospheric dust additions to soils are well documented in many parts of the world but not in the midwestern united states we investigated elemental mass fluxes associated with soil development in late wisconsinan loess in illinois and minnesota using zr as a stable index element positive mass fluxes of al fe and ti can most plausibly be explained by additions to these soils of fine far traveled dust with higher al zr fe zr and ti zr ratios than the coarser locally derived loess high resolution particle size analyses support this explanation the proposed dust influx will complicate efforts to quantify weathering processes in these soils far traveled dust influx could have occurred simultaneously with the final phase of local loess deposition and or later in the holocene depending on the timing of dust influx many other soils of the region may have been affected by it

optical ages on loess derived from outwash surfaces constrain the advance of the laurentide ice sheet out of the lake superior basin usa abstract we present textural and thickness data on loess from 125 upland sites in west central wisconsin which confirm that most of this loess was derived from the sandy outwash surfaces of the chippewa river and its tributaries which drained the chippewa lobe of the laurentide front during the wisconsin glaciation mis 2 on bedrock uplands southeast of the widest outwash surfaces in the chippewa river valley this loess attains thicknesses 5 m osl ages on this loess constrain the advance of the laurentide ice from the lake superior basin and into west central wisconsin at which time its meltwater started flowing down the chippewa drainage the oldest mar osl age 23 8 ka from basal loess on bedrock agrees with the established but otherwise weakly constrained regional glacial chronology basal ages from four other sites range from 13 2 to 18 5 ka pointing to the likelihood that these sites remained geomorphically unstable and did not accumulate loess until considerably later in the loess depositional interval other osl ages from this loess taken higher in the stratigraphic column but below the depth of pedoturbation range to nearly 13 ka suggesting that the chippewa river valley may have remained a loess source for several millennia

possible formation mechanisms for the modal coarse silt quartz particles in loess deposits abstract the first major event in the formation of a loess deposit is the production of silt sized quartz particles many particle production methods have been proposed the bulk of loess particles appear to be produced by a glacial grinding to give ice sheet loess or b cold weathering in high regions to give mountain loess there are close relationships between mountain loess and desert loess loess material can be seen as a product of the cold phase of the glacial cycle

transport direction of wisconsinan loess in southeastern minnesota a study of wisconsinan loess in part of southeastern minnesota confirms earlier suggestions that much of the loess in this region was not derived flora the floodplain of the mississippi river two wisconsinan loess units the peoria loess and roxana silt occur in the study area peoria loess 1 8 m thick fines systematically eastward from an abrupt western border toward the mississippi there are no apparent grain size trends away from other adjacent rivers peoria loess thickness generally decreases eastward but is highly variable probably because of differential erosion potential sources for this unit are pre wisconsinan sediments on the iowan erosion surface immediately west of the border of thick loess and wisconsinan glacial sources tens or hundreds of kilometers to the west the underlying roxana silt up to 1 m thick occurs only near the mississippi and fines away from that river the roxana silt deposit could reflect aggradation of the mississippi floodplain because of glacial activity upstream and does not have clear implications for upland vegetation near the study area by contrast transport of the peoria loess from distant glacial sources or wind erosion of upland surfaces closer to the loess deposit both imply extensive very sparsely vegetated surfaces west of the study area when the peoria loess accumulated

late quaternary aeolian dust input variability on the chinese loess plateau inferences from unmixing of loess grain size records abstract the grain size distributions gsds of loess paleosol sequences may provide valuable information on provenance transport and paleoclimate variability and consequently a wide range of methods to extract genetic information from loess gsds has been proposed here it is shown that a genetically meaningful decomposition of a series of late quaternary loess grain size records extending across the chinese loess plateau can be accomplished with the end member modelling algorithm emma the unmixing results in conjunction with loess accumulation rate estimates reveal that two contrasting dust supply patterns were active over the loess plateau during the last glacial interglacial cycle i a background sedimentation pattern that was dominant during interglacial periods especially over the central and southern parts of the loess plateau is reflected by the constant flux of the fine grained loess component ii an episodic highly variable dust input pattern that was dominant during glacial periods throughout the loess plateau and noticeable during interglacial periods mainly over the northern loess plateau and almost disappearing over the southern loess plateau is reflected in the admixture of two coarse grained loess components a genetic interpretation and the paleoclimatic significance of the mixing model are provided by comparison of the modelled end members with modern dust samples in terms of their gsd and flux rates

weathering of glauconite in soils of temperate climate as exemplified by a luvisol profile from gora pulawska poland abstract the aim of the research reported herein was to study the weathering of glauconite taking place in a luvisol profile developed on quartz glauconitic sand in gora pulawska eastern poland using x ray diffractometry fourier transform infrared spectroscopy mossbauer spectroscopy sem eds and an optical microscope the bulk soil material contains quartz glauconite glauconite smectite mixed layered minerals rich in smectite layers and traces of feldspars when compared with the parent material the cg horizon the bt1 and bt2 horizons are enriched in clay minerals while the ap aeg and e horizons are depleted in clays the observed mineral distribution is most likely controlled by the weathering of clay minerals in the uppermost part of the profile and translocation of clay fractions down the profile lessivage however contamination with glaciofluvial and or aeolian material has to be taken into consideration according to the microscopic observations of the thin sections clay is present in the bcg and cg horizons in the form of clay coatings and clay infilings this indicates that initially the parent sand did not contain clay fraction the fraction was formed most likely in the upper part of the soil profile and was deposited in the lower horizons by percolating atmospheric water green pellets separated from all the soil horizons are composed of glauconite showing more or less uniform chemical composition while clay fractions from all the horizons contain glauconite and glauconite smectite fine clay fractions separated from ap and aeg horizons are enriched in glauconite smectite relative to the fractions separated from the lower horizons the presence of glauconite and glauconite smectite minerals in the clay fractions studied indicates that glauconite weathering in the soil studied involves formation of glauconite clay by the pellet disintegration and glauconite smectitization ferrous iron accounts only for

pedogenesis by upbuilding in an extreme leaching and weathering environment and slow loess accretion south westland new zealand abstract soil formation is usually envisaged as acting from the surface downwards in many environments however the accumulation of sediment and soil formation are contemporaneous it is only where the rate of one process far exceeds the rate of the other that assumptions of topdown pedogenesis are appropriate the aspect of upbuilding pedogenesis that distinguishes it from topdown pedogenesis is that each increment of soil below the a horizon has experienced processes characteristic of all horizons above it this study examines the influence of upbuilding soil formation in a high rainfall environment of rapid soil formation and slow loess accretion an environment where upbuilding could have a noticeable influence on soil properties soils formed by topdown soil formation topdown soils are compared with soils formed in loess that accumulated from early last glaciation to the holocene upbuilding soils soils are compared in two environments alaquods on poorly drained terraces and placorthods or dystrochrepts on well drained moraine crests we have assumed that properties of the upbuilding soils inherited during the current topdown phase of pedogenesis beginning in the holocene are analogous to those in the topdown soils in this manner soil properties evolved during upbuilding are distinguished in well drained upbuilding soils on moraines subsoil organic carbon has mineralised so that profile trends are very similar to corresponding topdown soils upbuilding has enhanced weathering in subsoils which is reflected in lower ph lower total p and lower primary inorganic p than in topdown soil counterparts total p concentrations in upbuilding soils are much lower than unweathered loess and constant throughout the subsoil and there is almost no p in primary forms in contrast total p in c horizons of topdown soils reaches concentrations typical of the parent material and more than 30 of this is in a primary inorganic form the differences are attributed to each subsoil increment of upbuilding soils having been part of acid a and e horizons oxalate extractable fe and al data indicate that podzolisation was active during upbuilding poorly drained upbuilding soils on terraces have higher subsoil organic carbon inherited from former a or o horizons than comparable topdown soils buried a and o horizons inherited during upbuilding and preserved in the reducing conditions have acted as sinks for mobile al and now resemble podzolic illuvial bh horizons upbuilding through addition of loess to soils promotes a pedogenic pathway distinct from topdown pedogenesis consequently soil chronosequence studies that include soils on old loess mantled surfaces do not strictly satisfy the assumptions of soil chronosequences the nature and rate of soil processes inferred from these studies need revisiting the findings of this study are transferable to other environments where the rate of soil formation and sediment accumulation are comparable

impact of hydrologically driven hillslope erosion and landslide occurrence on soil organic carbon dynamics in tropical watersheds the dynamics of soil organic carbon soc in tropical forests play an important role in the global carbon c cycle past attempts to quantify the net c exchange with the atmosphere in regional and global budgets do not systematically account for dynamic feedbacks among linked hydrological geomorphological and biogeochemical processes which control the fate of soc here we quantify effects of geomorphic perturbations on soc oxidation and accumulation in two adjacent wet tropical forest watersheds underlain by contrasting lithology volcaniclastic rock and quartz diorite in the luquillo critical zone observatory this study uses the spatially explicit and physically based model of soc dynamics tribs eco triangulated irregular network based real time integrated basin simulator erosion and carbon oxidation and measurements of soc profiles and oxidation rates our results suggest that hillslope erosion at the two watersheds may drive c sequestration or co2 release to the atmosphere depending on the forest type and land use the net erosion induced c exchange with the atmosphere was controlled by the spatial distribution of forest types the two watersheds were characterized by significant erosion and dynamic replacement of upland soc stocks results suggest that the landscape underlain by volcaniclastic rock has reached a state close to geomorphic equilibrium and the landscape underlain by quartz diorite is characterized by greater rates of denudation these findings highlight the importance of the spatially explicit and physical representation of c erosion driven by local variation in lithological and geomorphological characteristics and in forest cover this article is protected by copyright all rights reserved

impact of holocene dust aggradation on a horizon characteristics and carbon storage in loess derived mollisols of the great plains usa the amount and vertical distribution of soil organic carbon soc storage is primarily a function of vegetation type and climate with influence from soil and landscape properties and human activities the influence of dust aggradation on landscapes during the holocene has largely been ignored as a factor in long term soc storage dust aggradation is important to soil horizonation and c sequestration since the dust deposit buries the landscape and increases solum thickness mollisols on loess covered upland tables in central nebraska have aggraded throughout the holocene as bignell loess accumulated above the late pleistocene brady soil in the loess tablelands the thickness of mollic colors a horizon properties and soc storage all decrease with distance from the source of bignell loess which is along a gradient of increasing precipitation for example along a 140 km transect of decreasing bignell loess thickness and increasing rainfall total thickness of a horizons decreases by 70 cm and the thickness of mollic colors decreases by 93 cm total soc storage decreases from 17 5 to 7 7 kg m2 a portion of the soc in subsurface horizons of modern soils was likely inherited from the brady soil which probably formed in a climate different than the present suggesting that soc storage is probably not in equilibrium with modern climatic conditions dust aggradation on a biologically active surface in a steppe environment has affected horizonation pigmentation and soc storage in central great plains loess derived mollisols

loess studies in central united states evolution of concepts abstract few words in the realm of earth science have caused more debate than loess it is a common term that was first used as a name of a silt deposit before it was defined in a scientific sense because this loose deposit is easily distinguished from other more coherent deposits it was recognized as a matter of practical concern and later became the object of much scientific scrutiny loess was first recognized along the rhine valley in germany in the 1830s and was first noted in the united states in 1846 along the lower mississippi river where it later became the center of attention the use of the name eventually spread around the world but its use has not been consistently applied over the years some interpretations and stratigraphy correlations have been validated but others have been hotly contested on conceptual grounds and semantic issues the concept of loess evolved into a complex issue as loess and loess like deposits were discovered in different parts of the us the evolution of concepts in the central us developed in four indefinite stages the eras of 1 discovery and development of hypotheses 2 conditional acceptance of the eolian origin of loess 3 bandwagon popularity of loess research and 4 analytical inquiry on the nature of loess toward the end of the first era around 1900 the popular opinion on the meaning of the term loess shifted from a lithological sense of loose silt to a lithogenetic sense of eolian silt however the dual use of the term fostered a lingering skepticism during the second era that ended in 1944 with an explosion of interest that lasted for more than a decade in 1944 r j russell proposed and h n fisk defended a new non eolian property based concept of loess the eolian advocates reacted with surprise and enthusiasm each side used constrained arguments to show their view of the problem but did not examine the fundamental problem which was not in the proofs of their hypothesis but in the definition of the term between 1944 and about 1950 the debates about loess reached a maximum level of complexity the main semantic problem was submersed in peripheral arguments about physical properties and genetic interpretations the scholarly treatment of the subject by fisk and russell stimulated quality responses from a diversity of earth scientists interested in academic and applied studies particularly geo history pedology soil mechanics and stratigraphy the long lasting popularity of loess studies during the bandwagon era lasted to about 1970 by that time the analytical and technical interests had attracted the mainstream into the fourth era with a focus beyond the old arguments although fisk and russell found themselves defending an unpopular theory they stimulated a scientific interest in the late quaternary history of the mississippi valley that may never be exceeded

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

clay mineralogy and chemistry of argillic horizons fragipans and paleosol b horizons of soils on a loess thinning transect in southwestern indiana usa abstract in southwestern indiana peorian loess about 20 000 years old thins eastward from the river valleys where it originated and covers sangamon paleosols developed in various parent materials where the loess is thick more than about 2 5 m the entire modern soil profile formed in loess and where it is thin the modern soil and paleosol are contiguous i e welded the objectives of this study were to determine how the mineralogy of the argillic bt horizons of modern soils changes with loess thickness how fragipan horizons bx formed in loess differ from non fragipan horizons formed in loess and how paleosol btb horizons differ from bt horizons and from each other soils were sampled on stable landscape positions along a loess thinning transect about 160 km long free oxides al d fe d si d were extracted with a citrate bicarbonate dithionite solution clay mineralogy was determined qualitatively by x ray diffraction and quantitatively by thermal and chemical methods in the loess derived bt horizons kaolinite content tends to increase and smectite to decrease as loess thins fragipans formed where loess is of intermediate thickness have higher contents of smectite and free silica greater surface area and higher exchangeable mg ca ratios than argillic horizons formed in loess high si d clay and si d fe d ratios are indicators of fragipan development paleosol btb horizons have higher base saturation than modern bt horizons they also contain more kaolinite and less smectite than bt horizons but the paleosols developed in different materials all have similar mineralogy

late pleistocene climate record in the eustis loess section nebraska based on land snail assemblages and magnetic susceptibility abstract based on multivariate analysis of mollusk assemblages and magnetic susceptibility of the eustis section in western nebraska the climate of the peoria loess steppe was relatively mild and in terms of annual precipitation relatively moist during the advance stages of woodfordian ice it was cold and dry during ice retreat the diversity and composition of mollusk species indicates that the extreme cold and dry climate was reached during the late phase of peoria time in mollusk zone mz3 although soil moisture during the growing season at that time was high the growing season was short and annual precipitation totals were low low values of magnetic susceptibility imply relatively rapid dust deposition during this interval judging from the current ecological tolerance of the species no closed forest existed in the area only scattered shrubs or isolated tree stands may have been present the late peoria mz3 assemblage compares favorably with the columella fauna of europe in contrast the early peoria mollusk assemblages mz1 and mz2 compare well with the european pleniglacial pupilla associations based on available 14 c dates from the studied region and on assumed relation of magnetic susceptibility to sedimentation rates the estimated age of the mz1 and mz2 zones is 24 000 to 16 000 yr whereas that of mz3 is 16 000 to 12 000 yr

chronostratigraphy of silt dominated pleistocene periglacial slope deposits on mt śleza sw poland palaeoenvironmental and pedogenic significance abstract slope deposits with aeolian silt admixture are a widespread parent material of soils in the temperate zone but may be neglected when rates of soil production are quantified the concept of periglacial cover beds differentiates slope deposits with or without aeolian silt admixture yet there is a remaining debate on processes and the timing of their formation a previous study done by us at mt leza sw poland concluded that slope deposits with variable aeolian silt admixture or its lack have a significant influence on the pathway of soil formation the present work builds upon this finding by adding further granulometric and micromorphological data from three representative profiles along a toposequence in order to refine our understanding of local slope deposits and soil formation additionally seven numerical ages using luminescence dating provide a chronological framework for our reconstructions and allow linking the forming processes of these pedosedimentary records to regional palaeoenvironmental conditions the oldest aeolian deposits are of middle pleistocene age 280 19 ka with interlayered palaeosol marine isotope stage mis 9 or older late pleistocene slope deposits encompass the maximum loess thickness and are dated to mis 2 luminescence ages from the upper layers indicate shallow reworking which we tentatively correlate to the younger dryas yd two profiles with thick loess mantles have strong clay illuviation features presumably formed during the holocene however weak clay illuviation in the third profile with a thin loess mantle having an age of yd over granite regolith seems to have occurred before the holocene as only fragmented clay coatings probably mis 2 pedogenesis could be found

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

the belotinac section southern serbia at the southern limit of the european loess belt initial results abstract the palaeoclimate record preserved in loess deposits in s serbia is poorly understood this is in strong contrast to the situation in the north of the country vojvodina region where similar deposits have been intensively investigated in recent years this study presents a first detailed description initial proxy analysis magnetic susceptibility colour total organic carbon and preliminary luminescence chronology of a loess palaeosol sequence that is exposed in an abandoned quarry at belotinac near the city of nis s serbia the sequence is about 10 m thick and preserves three loess units and three weakly developed palaeosol units although its potential remains to be fully tapped the preliminary results demonstrate that the sequence offers a unique record of climate and environmental change during the late pleistocene at the transition between mediterranean and continental europe

geomorphology of the chippewa river delta of glacial lake saginaw central lower michigan usa abstract we introduce characterize and interpret the geomorphic history of a relict pleistocene aged delta of the chippewa river in central lower michigan the broad sandy chippewa delta developed into various stages of glacial lake saginaw between ca 17 and 15 ka bp calibrated ages although the delta was first identified in 1955 on a statewide glacial geology map neither its extent nor its pleistocene history had been previously determined the delta is typically forested owing to its wet sandy soils which stand out against the agricultural fields of the surrounding loamy lake plain sediments the delta heads near the city of mt pleasant and extends eastward onto the saginaw lowlands i e the plain of glacial lake saginaw data from 3285 water well logs 180 hand augered sites and 185 points randomly located in a gis on two storied sand over loam soils were used to determine the extent textural properties and thickness of the delta the delta is 18 km wide and 38 km long and is sandy throughout deltaic sediments from neighboring rivers that also drained into glacial lake saginaw merge with the lower chippewa delta obscuring its boundary there the delta is thickest near the delta s head and in the center but thins to 1 2 m or less on its eastern margins mean thicknesses are 2 3 2 9 m suggestive of a thin sediment body frequently impacted by the waves and fluctuating waters of the lakes although beach ridges are only weakly expressed across the delta because of the sandy sediment the coarsest parts of the delta are generally coincident with some of these inferred former shorezones and have a broad incised channel that formed while lake levels were low the thick upper delta generally lies above the relict shorelines of glacial lakes saginaw and arkona 17 1 to 16 ka bp whereas most of the thin distal delta is associated with glacial lake warren 15 ka bp together these data suggest that the chippewa delta formed and prograded as lake levels in the saginaw lowlands alternated and episodically fell the result is a delta that is comparatively thin expansive and sandy in some places these sands have subsequently been reworked into fields of small parabolic dunes

location and expression of fragic soil properties in a loess covered landscape southern illinois usa abstract fragic soil properties often develop in thin loess units overlying residual parent materials in the midwest usa morphologic indicators of these fragic properties are often weakly expressed making consistent mapping of soils difficult this study was initiated in a small watershed in union county illinois to determine location and degree of development of fragic materials and fragipans on the landscape we also sought to assess factors influencing the degree of expression of these features and document accessory soil properties that reflect the presence of these fragic soil materials nine pedons from two catenas were sampled and selected chemical physical and mineralogical analyses were conducted results indicate that loess thickness across the watershed ranged from about 2 to 4 m fragic soil properties were observed in argillic horizons on side slope and head slope geomorphic components at depths ranging from 51 to 111 cm depths to horizons meeting fragipan criteria ranged from 140 to 175 cm discontinuity between two loess units peoria and roxana silts was verified by both particle size analysis fine coarse silt ratios clay free fine and coarse silt and magnetic susceptibility these data suggest that the development of fragic soil properties is not controlled solely by the discontinuity between loess deposits fragipans are weakly developed based on rupture resistance morphological features such as structure bulk density

elucidating the geogenic and pedogenic pathways of formation of soils of peninsular india signatures of past landscape modifications abstract the soils of modified landforms of peninsular india present an opportunity to unearth soil and landscape evolution we explore the potential of vertical texture contrast vtc soils as signatures of past landscape modifications and associated soil formation in peninsular india we studied six vtc soils occurring on different geological formations for their morphology geochemistry and mineralogy in order to interpret the geogenic and pedogenic pathways of their formation the presence of a lithological discontinuity with sharp contrast in particle size in pedons p1 and p3 suggested that fluvial sedimentary layering led to their formation pedons p2 and p5 are examples of buried soils where basaltic alluvium of varying thickness is overlying the soils of granitic and gneissic complex origin these soils are potential proxies of landform changes attributable to paleo alluvial mass deposition possibly during the late pleistocene pedon p4 is a relict paleosol in which the presence of a ck horizon between the argillic bt and bc horizons indicates sedimentation of stratified rocks geogenic followed by clay illuviation pedogenic during the past wet climate the occurrence of smectite dominant shrink swell s w soil pedon p6 over the shale parent material suggests that the s w soil is from a transported alluvium of weathering deccan basalt our results demonstrate the usefulness of vtc soils in interpreting the climate shift driven soil landscape evolution in peninsular india and elsewhere

holocene loess deposition and soil formation as competing processes matanuska valley southern alaska although loess paleosol sequences are among the most important records of quaternary climate change and past dust deposition cycles few modern examples of such sedimentation systems have been studied stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the matanuska valley in southern alaska show that loess deposition there began sometime after f6500 14 c yr b p and has continued to the present the silts are produced through grinding by the matanuska and knik glaciers deposited as outwash entrained by strong winds and redeposited as loess over a downwind distance of f40 km loess thickness sand content and sand pluscoarse silt content decrease whereas fine silt content increases loess deposition was episodic as shown by the presence of paleosols at distances 10 km from the outwash plain loess source stratigraphic complexity is at a maximum i e the greatest number of loesses and paleosols at intermediate 10 25 km distances from the loess source surface soils increase in degree of development with distance downwind from the source where sedimentation rates are lower proximal soils are entisols or inceptisols whereas distal soils are spodosols ratios of mobile cao k2o and fe2o3 to immobile tio2 show decreases in surface horizons with distance from the source thus as in china where loess deposition also takes place today eolian sedimentation and soil formation are competing processes study of loess and paleosols in southern alaska shows that particle size can vary over short distances loess deposition can be episodic over limited time intervals and soils developed in stabilized loess can show considerable variability under the same vegetation d 2004 university of washington all rights reserved

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

pedogenetic interpretations of particle size distribution curves for an alpine environment abstract the qilian mountains are generally capped by a productive silty soil layer wherever the environment allows as holocene loess is prevalent across the qilian mountains we assume that at least some of these fine sediments are derived from loess deposition and that soils across the region may be genetically linked to test these hypotheses nine pedons in different landscapes within a typical alpine watershed of the qilian mountains were sampled we also collected fine earth samples from glacier surfaces and crevices of glacial debris in the moraine zone the particle size distribution psd is used as a proxy for identifying aeolian fractions in soils the psd curves of all of the fine earth fractions examined are polymodal although three modal sizes of roughly 16 m 35 m and 80 m are found in almost all sediments in varying proportions these modal sizes have been identified as three sources of aeolian sediments in different transport systems the composition and thickness of loess sediments are related to local site conditions and may be related to the paleoenvironmental history of the site clastic debris and vegetation cover serve as dust traps during different stages of soil formation in this alpine environment and soils grow upward with accumulating loess sediment our study demonstrates that psd curves can be used to determine the origins and especially aeolian origins of soils furthermore this study provides insight into the pedology ecology and paleoenvironmental history of loess affected ecosystems in alpine areas of the qinghai tibetan plateau

unprecedented last glacial mass accumulation rates determined by luminescence dating of loess from western nebraska abstract a high resolution chronology for peoria last glacial period loess from three sites in nebraska midcontinental north america is determined by applying optically stimulated luminescence osl dating to 35 50 m quartz at bignell hill nebraska an osl age of 25 000 yr near the contact of peoria loess with the underlying gilman canyon formation shows that dust accumulation occurred early during the last glacial maximum lgm whereas at devil s den and eustis nebraska basal osl ages are significantly younger 18 000 and 21 000 yr respectively at all three localities dust accumulation ended at some time after 14 000 yr ago mass accumulation rates mars for western nebraska calculated using the osl ages are extremely high from 18 000 to 14 000 yr much higher than those calculated for any other pre holocene location worldwide these unprecedented mars coincide with the timing of a mismatch between paleoenvironmental evidence from central north america and the paleoclimate simulations from atmospheric global circulation models agcms we infer that the high atmospheric dust loading implied by these mars may have played an important role through radiative forcing in maintaining a colder than present climate over central north america for several thousand years after summer insolation exceeded present day values

the geomorphology sediment distribution soil formation nexus on the northeastern qinghai tibetan plateau implications for landscape evolution abstract the interactions between geomorphology sediment distribution and soil development in alpine regions are poorly understood in this study we analyzed the spatial variations of different sediment types and corresponding soils in 15 pedosedimentary profiles across three major geomorphic units in an alpine ridge valley basin of the qilian mountains northeastern qinghai tibetan plateau particle size distribution was used to trace the sediment types inorganic and organic carbon concentrations were included as metrics of soil processes aeolian silts from both distant and proximal sources cover floodplains hillslopes and some positions on alluvial fans while the distribution of fluvial sediments and periglacial slope deposits are much more limited due to the coverage of loess the soils vary in response to sediment types and climatic conditions under the influence of their geomorphic settings the vertical distribution patterns of carbonates in soil profiles show considerable differences among different geomorphic units reflecting their contrasting water balance and migration pathways soil organic carbon accumulates most extensively in aeolian silts with sufficient water supply a special pedogenic soil horizon the mattic epipedon is formed primarily in loessial sediments in kobresia ecosystems the complex entanglement of fine earths and massive grassroots make the mattic epipedon extremely resilient which helps to preserve the soils and to shape the landscapes by integrating geomorphology sedimentology ecology and pedology the outcomes of this study promote the understanding of the evolution of typical landscapes and ecosystems of the northeastern qinghai tibetan plateau and many other periglacial settings