holocene loess in illinois revealed by osl dating implications for stratigraphy and geoarchaeology of the midwest united states abstract most uplands in illinois are blanketed by late wisconsinan peoria loess and the conventional wisdom is that little or no dust accumulation occurred during the holocene 11 7 ka to present in a recent effort to investigate if illinois holocene loess was deposited and preserved we applied optically stimulated luminescence osl dating to seven locations where loess is thick these include four sites along the mississippi river in westernmost illinois and three loess bluffs south of the illinois river in central illinois our results suggest that holocene aged loess is preserved along the mississippi river in the state of illinois in contrast no holocene loess was found south of the illinois river in the central portion of the state in addition to its spatially limited distribution holocene loess thicknesses range only up to 1 m nevertheless loess stratigraphy and osl dating results provide the first holocene loess reported east of the missouri river our new finding also resolves the long time archeological puzzle that a number of artifacts of several thousand years old were buried by upland loess along the mississippi river

palaeosecular variation in central mexico over the last 30 000 years the record from lavas summary 13 lava flows of known age ages from i4c dating which have been erupted in the last 30000 years have been studied to determine the palaeosecular variation of the geomagnetic field in central mexico samples were taken from two different monogenetic volcanic fields the michoacan guanajuato volcanic field six sites and the chichinautzin formation seven sites both part of the transmexican volcanic belt the lavas were studied in detail using rock magnetic methods magnetic susceptibility at room temperature low temperature susceptibility behaviour hysteresis loops curie temperatures combined with reflected light microscopy in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals the magnetic carriers are titanomagnetites which show differing degrees of high temperature deuteric oxidation and seem to be predominantly pseudo single domain psd though in many cases are probably a mixture of domain states mean palaeomagnetic directions and palaeointensity values using shaw and thellier techniques were obtained using several specimens from each flow our data seem to indicate a sharp easterly swing in declination about 5000 years ago which is also observed in lake sediments from central mexico the calculated values of the virtual dipole moment vdm range from 3 1 to 14 9 x a m2 our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr with a peak at about 9000 years bp these are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field

detransformation of the british geomagnetic secular variation record for holocene times in this note we replot the british post glacial secular variation curve in terms of actual values of declination and inclination rather than the transformed declination and inclination system used in our original paper turner thompson 1981 this should facilitate the comparison of our record with contemporaneous european archaeomagnetic data our composite record was obtained by averaging the dated records from 10 cores of lake sediment the sequence of unit vectors describing the magnetic direction record of each core was rotated so as to place its mean direction the mean over the section of core dated between 0 and 7000 bp the time span of the shortest core at zero transformed declination and inclination dt o it 0 the transformed coordinate frame of each core is thus derived from its mean direction assumed to represent the mean geomagnetic field direction over the 7000 yr period rather than from the core tube and its orientation during coring hence the problem of not knowing the azimuthal orientation and inclination of the corer during core collection is avoided and the 10 records can be averaged in this coordinate system transformed coordinates then provide a convenient generalised method of plotting averaged sediment records however in the archaeomagnetic method sample orientation is straightforward and the results can readily be plotted as absolute declination and inclination values so for consistency when comparing the two we have attempted here to detransform our record the following procedures assumptions and approximations were taken to produce the detransformed magnetograms and bauer type plots of figs 1 and 2 1 amplitude correction although the combination of 10 data sets produces a good estimate of the signature of the geomagnetic variations the following factors contribute to an overall loss of amplitude in both declination and inclination a the quality of magnetic recording varies widely between different sediments depending on the porosity of the sediment the size and shape distributions and the nature of the magnetic carrier verosub 1979 the loch lomond sediments carry a good high amplitude pattern of remanent directions of which the most recent closely follow the london observatory records the much wetter and less compacted sediments of llyn geirionydd on the

stratigraphy morphology and geochemistry of late quaternary buried soils on the high plains of southwestern kansas usa abstract this study investigated two stratigraphic sequences that record the complex interplay of sedimentation and pedogenesis over the past ca 84 ka on the high plains of southwestern kansas up to eight eolian sand and loess units with associated soils were identified in two cores collected from an upland setting soil morphological and geochemical data were used to quantitatively assess and compare soil development between multiple buried soils chronostratigraphic relationships indicate that 1 loess and eolian sands were episodically deposited during late marine isotope stage mis 5 ca 84 70 ka 2 the sangamon soil at this site formed between mis 3 4 ca 70 52 ka which is consistent with age estimates for renewed sangamon pedogenesis in the mississippi river valley and 3 soil development in the gilman canyon formation began at ca 44 ka and continued until at least 29 2 ka multiple lines of evidence including grain size distributions structure clay content and chemical weathering index data indicate that the morphology and chemistry of the ak horizon developed in the gilman canyon formation is a product of cumulization by slow loess additions similar evidence suggests that cumulization processes are also responsible for the morphology and chemistry of other buried soils in the stratigraphic sequence overall loess inputs during pedogenesis complicate the quantification of weathering processes in these soils

modern sangamon and yarmouth soil development in loess of unglaciated southwestern illinois abstract the thebes section in unglaciated southwestern illinois contains a well preserved 500 kyr loess paleosol sequence with four loesses and three interglacial soils various magnetic mineralogical and elemental properties were analyzed and compared over the thickness of soil sola these proxies for soil development intensity have the following trend yarmouth geosol sangamon geosol modern soil quartz plagioclase zr sr and tio 2 na 2 o ratios were most sensitive to weathering frequency dependent magnetic susceptibility and anhysteretic remanent magnetization greatest in a horizons also correspond well with soil development intensity neoformed mixed layered kaolinite expandables suggestive of a warm humid climate were detected in the sangamon and yarmouth soil sola clay illuviation in soils was among the least sensitive indicators of soil development differences in properties among interglacial soils are interpreted to primarily reflect soil development duration with climatic effects being secondary assuming logarithmic decreases in weathering rates the observed weathering in the sangamon geosol is consistent with 50 kyr of interglacial weathering oxygen isotope stage 5 compared to 10 kyr for the modern soil oxygen isotope stage 1 we propose that the yarmouth geosol in the central midwest formed over 180 kyr of interglacial weathering including oxygen isotope stages 7 9 and 11

comparison of paleoclimatic change from zr rb ratios in chinese loess with marine isotope records over the 2 6 1 2 ma bp interval 1 the loess paleosol sequences in north china act as a key archive in the study of continental paleoclimatic change over the last 2 6 ma however the correlation between the continental loess records and the marine sediments over the 2 6 1 2 ma bp interval is poorly studied in this paper zr and rb concentrations were measured on samples taken at 20 cm intervals from the lingtai section over the interval from 2 6 1 2 ma bp because zr is enriched in coarse grain fractions whereas rb is enriched in the fine fractions which are retained during loess pedogenesis the zr rb in loess can reflect the original grain size variation and serve as a proxy for winter monsoon strength our zr rb ratios over the interval from 2 6 1 2 ma bp generally match the marine 18o record especially during the 1 9 1 2 ma bp interval strong 400 ka periodicity cycles found in the loess zr rb ratio record are similar to the marine 13c record suggesting a possible low latitude influence on the paleoclimatic regime during this interval

deciphering complex soil site formation in sands abstract this paper summarizes aspects of the geoarchaeological research at two adjacent multi component archaeological sites 13jp86 and 13jp87 along indian creek in central iowa usa the sites both recently salvaged but now destroyed formed in late pleistocene sands reworked from glacial sediments that emanated from the wasting des moines lobe glacier some 13 000 14 000 years ago the soils contained shallowly dispersed and mixed artifacts that span the paleoindian to historic cultural spectrum in open areas as at indian creek site formation processes equate to natural soil genetic processes plus human imprints cultural materials once deposited become part of the soil and subject to dynamic soil processes these soils had reasonably well expressed ap a and e horizons that collectively formed thick one layered biomantles underlain by well expressed argillic bt horizons the biomantles had been well bioturbated deeply in some pedons but still exhibited organized a and e horizons the bt horizons were also bioturbated though less so and consisted of multiple thin to thick sandy clay bands termed illuvial clay lamellae icl s the icl s contained modest to appreciable amounts of illuvial clay as bridges between grains and as diffuse splotches and blebs separated by less clayey e horizon like interlamellar sandy zones deeper and less bioturbated e like sandy zones had accumulated so much clay that they had coalesced with icl s into thick complexly banded argillic bt horizons the process histories of the sandy pedons were obviously extremely complex the geoarchaeological aspects of the project which were mainly complex pedologic ones were largely interpreted by drawing on the genetic principles of dynamic denudation to explain soil site evolution many questions were raised and most were answered under these principles new concepts and perspectives were gained in this study and the resulting interpretive scenarios carry explanatory implications for sandy soils everywhere whether charged with cultural materials or not

a rock and paleomagnetic study of a holocene lava flow in central mexico abstract magnetic measurements of the tres cruces lava flow ca 8500 years bp central mexico show the presence of two remanence carriers a ti rich titanomagnetite with a curie temperature between 350 and 400 c and a ti poor magnetite with a curie temperature close to 580 c magnetic changes after heating indicate that the titanomagnetite exsolves into magnetite and ilmenite when the sample is heated to 580 c paleointensity estimates with the thellier and thellier method thellier e thellier o 1959 sur l intensite du champ magnetique terrestre dans le passe historique et geologique ann geophysique 15 285 376 were only successful up to temperatures of 350 to 400 c this temperature corresponds with the curie temperature of the titanomagnetite which is probably pseudo single or multi domain therefore the paleointensities should be interpreted with caution the magnetic composition changes after 580 c heating may explain the large variations in previous paleointensity determinations for the tres cruces rocks gonzalez s sherwood g bohnel h schnepp e 1997 palaeosecular variation in central mexico over the last 30 000 years the record from lavas geophys j int 130 201 219 using the shaw method shaw j 1974 a new method of determining the magnitude of the palaeomagnetic field application to five historic lavas and five archaeological samples geophys j r astr soc 39 133 141

direct estimates of pedogenic magnetite as a tool to reconstruct past climates from buried soils 1 variations in magnetic properties of buried soils can be used to reconstruct past climatic conditions during paleosol formation most methods however are based on comparisons between the magnetically enriched upper soil horizons and the magnetically unaltered parent material in thin loess paleosol sequences such a comparison can be problematic because all horizons soil and underlying loess may be affected to varying degrees by pedogenesis we propose two direct estimates of pedogenic magnetite based on the analysis of anhysteretic remanent magnetization ratios carm isothermal remanent magnetization and coercivity distributions these estimates are independent of any information regarding the parent material and are possible if pedogenic minerals have similar magnetic properties throughout the study region this condition seems to be met throughout the midwestern united states and a few loessic soils elsewhere the remanence carrying part of pedogenic magnetite is composed of single domain particles with consistent well constrained magnetic properties these particles are extremely well dispersed in the soil matrix as indicated by the absence of noticeable magnetostatic interaction effects our analyses of over 70 modern loessic soil profiles demonstrate that the abundance of pedogenic magnetite correlates well with modern climate and that the method is suited for reconstruction of past climates from paleosols

loess mantle spatial variability and soil horizonation southern wisconsin usa abstract loess is an important quaternary sediment that records evidence of landscape instability in sediment source areas and landscape stability in accumulation areas in wisconsin usa loess mantles glaciogenic deposits dating to the last glaciation but the landscape distribution and effects of the loess mantle on soil formation have received very little attention this study investigates the influence of glacial landforms on the spatial pattern of loess thickness and how the presence or absence of a loess mantle overlying glaciogenic sediments has influenced soil profile morphology namely thickness and nature of horizonation loess thickness follows systematic trends along hillslopes with slope percentage explaining most loess thickness variation between summit and backslope positions in the presence of a loess mantle solum and bt horizon thickness is proportional to the thickness of the loess mantle in well drained profiles in the absence of a loess mantle landscape and sediment characteristics that control permeability and water throughflow appear to be the most important determinants of profile characteristics the loess mantle modulates soil formation above the lithologic discontinuity with sandy calcareous glacial sediments by controlling soil water behavior and having physical and chemical characteristics conducive to transformation to soil genetic horizons

reconstruction of late pleistocene paleoenvironments in southern germany using two high resolution loess paleosol records abstract two loess paleosol sequences from the heilbronn basin in southwestern germany frankenbach and talheim have been investigated to gain information about environmental conditions during the last interglacial glacial cycle since paleoenvironmental research on terrestrial archives is crucial for a better understanding of past climatic and environmental conditions the profiles were studied using a multi proxy approach applied methods include the analyses of grain size distribution element contents sediment color rock magnetism micromorphology and black carbon bc via benzene polycarboxylic acids bpca the data reveal that the two profiles show large variations in conservation due to their different geomorphologic positions moreover the results imply a subarctic climate with stable conditions during the middle pleniglacial mis 3 in situ soil formation phase while the lower pleniglacial mis 4 was characterized by erosion and reworking of eemian and early glacial mis 5 material but also by accumulation of aeolian material during the late lower pleniglacial mis 4 in frankenbach the results further suggest that the rhine river floodplain has been a major source for the accumulated material in the two profiles which indicates westerly wind directions during the time of accumulation the low gsi and u ratio of upper pleniglacial mis 2 sediments supported by the overall high content of fine material imply a larger distance to the source area we give an overview of loess in the heilbronn basin and place it in a wider context of loess in western europe

using the accumulation of cbd extractable iron and clay content to estimate soil age on stable surfaces and nearby slopes front range colorado abstract in many transport limited environments morphology pedogenic iron and clay content provide a basis for estimating the exposure age of soils and associated landforms we measured citrate buffered dithionite cbd extractable fe fe d and clay concentration in fresh rock saprolite morainal and colluvial materials and soil horizons from stable surfaces and hillslopes in the colorado front range fresh igneous and high grade metamorphic rocks contain d and 1 to 5 clay as bedrock and surficial deposits age fe d and clay accumulate from weathering and dustfall late holocene regolith at warm dry sites contains small amounts of fe d and clay but relatively moist soils developed on early holocene cirque deposits contain as much as 1 5 fe d and 8 clay concentrations and total profile accumulation of fe d and clay increase with age in soils developed on stable surfaces of glacial deposits as old as 130 kyr on stable sites fe d and clay accumulation from weathering and dust is 0 02 g cm 2 kyr 1 and 0 2 g cm 2 kyr 1 respectively we used the fe d and clay inventory in soil profiles at dated stable front range surfaces to calculate accumulation functions which allowed us to estimate soil age at hillslope sites heterogeneous parent material particularly on hillslopes and climate related effects add to variability in measured relations mobile regolith in gordon gulch one of the boulder creek critical zone observatory czo catchments yields profile ages from about 0 5 to 5 10 4 yr comparable to values measured using other techniques calculated profile ages are older on a north vs south facing slope and increase from the drainage divide to the footslope ages calculated for stabilized colluvium and well developed buried profiles at nearby hillslope sites lefthand ward and rollinsville suggest that these soils have stabilized over periods 10 5 yr in the absence of radiometric ages the accumulation of fe d and clay in soils on stable sites and hillslopes provides a useful local chronofunction for 10 3 to 3 10 5 yr local footslope thickening of mobile regolith buried soils and areas of fe d and clay rich stabilized colluvium suggest that steady state models of hillslope regolith must be modified to account for observed soil properties

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

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

computer synthesis of geomagnetic palaeosecular variations computer models designed to synthesize palaeosecular variations of the geomagnetic field cast doubt on some widely accepted palaeomagnetic dogmas westward or eastward drift cannot be uniquely deduced from the sense of rotation of the geomagnetic vector the use of unit vectors in statistical analyses leads to systematic errors which render investigation of the global symmetry of the palaeofield more difficult than previously supposed at least some geomagnetic excursions may be regarded as large amplitude secular variations

watershed scale chemical weathering in a merokarst terrain northeastern kansas usa abstract carbonate weathering in the merokarst landscape at the konza prairie near manhattan ks is governed by kinetically rapid reaction rates similar to other carbonate settings the geology of the site consists of repeating couplets of shale and limestone mantled by pleistocene loess on which most soils are built the headwater stream that is the subject of this study is intermittent and well connected to the secondary porosity in the limestone aquifers such that the water chemistry is groundwater dominated despite increasing in situ weathering rates shown by increasing solute concentrations long term 21 of 24 years decline in stream water discharge has reduced chemical denudation the current chemical denudation rate is 0 02 mm yr 1 limestone bedrock thickness 26 6 m is 38 of total bedrock thickness 70 m the present landscape would have taken 1 4 million years to dissolve at current weathering rates despite paleogeographic reconstructions suggesting exposure for the past 260 ma estimates of the time to erode younger strata using current physical and chemical denudation rates are 80 159 ma still much less than the age of the rocks an alternate source of material dust is proposed that may slow limestone weathering which in turn protects shales from physical erosion thereby slowing landscape evolution

a soil chronosequence in the semi arid environment of patagonia argentina abstract soil development with time was investigated on beach ridges with ages ranging from about 1380 to 6240 14c years bp at the eastern coast of central patagonia the main pedogenic processes are accumulation of organic matter and carbonate leaching and accumulation within the upper part of the soils soil formation is strongly influenced by incorporation of eolian sediments into the interstitial spaces between the gravel of which the beach ridges are composed different amounts of eolian material in the soils lead to differentiation into leptosols containing 10 fine earth in the upper 75 cm and regosols containing 10 fine earth soil depth functions and chronofunctions of organic carbon calcium carbonate ph ca zr mg zr k zr na zr fe zr mn zr and si al obtained from x ray fluorescence analysis were evaluated to establish soil chronofunctions mean values of the horizon data of 0 10 cm below the desert pavement were used which were weighted according to the horizon thicknesses the depth function of ph shows a decrease towards the surface indicating leaching of bases from the upper centimeters chronofunctions of ph show that within 6000 radiocarbon years of soil development ph drops from 7 0 to 6 6 in the leptosols and from 8 1 to 7 5 in the regosols the higher ph of the regosols is due to input of additional bases from the eolian sediments chronofunctions of ca zr and k zr indicate progressive leaching of ca and k in the regosols showing close relationships to time r2 0 972 and 0 995 na leaching as indicated by decreasing na zr ratios shows a strong correlation to time only in the leptosols r2 0 999 both leptosols and regosols show close relationships to time for fe zr r2 0 817 and 0 824 mn zr r2 0 940 and 0 803 and si al 0 971 and 0 977 indicating enrichment of fe and mn and leaching of si leaching of mobile elements takes place on a higher level in the regosols than in the leptosols from the beginning of soil formation hence a significant part of the eolian sediments must have been incorporated into the beach ridges very soon after their formation

secular variation as recorded in lake sediments a discussion of north american and european results type curves depicting secular variations in declination and inclination through holocene time have been constructed by stacking data from individual cores of lake sediment from east central north america and the u k there is a strong positive correlation in declination with zero phase shift froiti 0 to 4500 14 c years b p but from 4500 to 8500 14 c years b p the correlation is strongly negative which we interpret in terms of fluctuations in intensity of standing geomagnetic sources a source located under the atlantic ocean appears to have been dominant before ca 4500 14c years b p and then another similar source located either to the east or to the west of both observation areas gained dominance however the inclination type curves show optimum positive correlation for a phase shift of ca 400 years suggesting that the geomagnetic sources that caused them were drifting westward at ca 0 2 degrees a year there is no way of adjusting the timescales so as to obviate this apparent paradox secular variations of the total geomagnetic vector have been investigated by noting the sense clockwise anticlockwise of looping of the v g p paths though this cannot be interpreted uniquely in terms of westward or eastward drifting sources in the core as demonstrated by specific radial dipole models

limnologic history of lago de patzcuaro michoacan mexico for the past 48 000 years impacts of climate and man abstract lago de patzcuaro lies at an elevation of 2035 m 19 36 n 101 39 w on the west part of the volcanic meseta central of mexico about 50 km east southeast of morelia pollen diatom and geochemical records from a 15 m core taken in 6 m of water continuously track vegetation and limnological changes in the patzcuaro basin for the past 48 ky calendar years pine oak and alder pollen dominate both the wisconsin and holocene vegetation record and indicate that this region did not witness strongly arid climates during that time before the holocene juniperus type and artemisia pollen document cooler climates of more effective moisture at least seasonally isoetes characterizes the full and late glacial interval 25 13 ka and implies along with the diatoms aulacoseira and stephanodiscus cool deep freshwater conditions at lago de patzcuaro the freshest and deepest lacustrine phase in the lake occurred 38 to 25 ka during this time lago de patzcuaro may have drained into the lerma river system between 30 and 10 ka diatom species that bloom in the winter and early spring imply moisture during those seasons evaluation of contemporaneous marine and terrestrial records west and east of lago de patzcuaro suggests that this moisture probably originated from westerly storm tracks shifted south by the laurentide ice sheet after 10 ka lago de patzcuaro became shallower and more eutrophic rooted aquatic plants prospered under a climate regime of negative hydrologic budgets increased seasonality and moisture arriving during the summer as it does today the lake became alkaline enough by the mid holocene to deposit ostracode rich marls at the core site for the first time in the past 48 ky indigenous agriculture in the patzcuaro drainage and around the lake appears about 4 ka with the appearance of zea and chenopodiineae pollen iron and potassium track increased soil erosion and planktic diatoms cyclostephanos record nutrients flushed into the lake from the drainage basin

compositions of modern dust and surface sediments in the desert southwest united states 1 modern dusts across southwestern united states deserts are compositionally similar to dust rich av soil horizons depths of 0 0 5 cm and 1 4 cm at 35 sites for common crustal elements but distinctly different for some trace elements chemical compositions and magnetic properties of the soil samples are similar among sites relative to dust sources geographic areas and lithologic substrates exceptions are li u and w enriched in owens valley california and mg and sr enriched in soils formed on calcareous fan gravel in southeast nevada the av horizons are dominated by dust and reflect limited mixing with substrate sediments modern dust samples are also similar across the region except that owens valley dusts are higher in mg ba and li and dusts both there and at sites to the north on volcanic substrates are higher in sb and w thus dust and av horizons consist of contributions from many different sources that are well mixed before deposition modern dusts contain significantly greater amounts of as cd cr cu ni pb and sb than do av horizons which record dust additions over hundreds to thousands of years these results suggest that modern dust compositions are influenced by anthropogenic sources and emissions from owens dry lake after its artificial desiccation in 1926 both modern dusts and av horizons are enriched in as ba cu li sb th u and w relative to average crustal composition which we interpret to indicate that the geologic sources of dust in the southwestern united states are geochemically distinctive

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

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

compositional trends in aeolian dust along a transect across the southwestern united states 1 aeolian dust strongly influences ecology and landscape geochemistry over large areas that span several desert ecosystems of the southwestern united states this study evaluates spatial and temporal variations and trends of the physical and chemical properties of dust in the southwestern united states by examining dust deposited in natural depressions on high isolated surfaces along a transect from the mojave desert to the central colorado plateau aeolian dust is recognized in these depressions on the basis of textural chemical isotopic and mineralogical characteristics and comparisons of those characteristics to the underlying bedrock units spatial and temporal trends suggest that although local dust sources are important to the accumulated material in these depressions mojave desert dust sources may also contribute depth trends in the depressions suggest that mojave sources may have contributed more dust to the colorado plateau recently than in the past these interpretations point to the important roles of far traveled aeolian dust for landscape geochemistry and imply future changes to soil geochemistry under changing conditions in far distant dust source areas

paleosecular variations recorded by holocene pleistocene sediments from lake el trebol patagonia argentina paleomagnetic studies carried out on six cores from the bottom sediments from lake el trebol south argentina are described measurements of directions declination and inclination d and i and intensity of natural remanent magnetisation nrm magnetic susceptibility at low and high frequency specific x and volumetric k isothermal remanent magnetisation irm saturation isothermal remanent magnetisation sirm back field and anhysteric remanent magnetisation arm were carried out stability of the nrm was investigated by alternating field demagnetisation rock magnetic studies suggest that the main carriers of magnetisation are ferrimagnetic minerals predominantly pseudo single domain magnetite records of nrm and k show a good correlation with the sedimentological description and also with those of shorter cores previously studied the tephra layers were identified from the lithologic profiles and also from the magnetic susceptibility logs due to their different chronological meaning and their rather bad behaviour as magnetic recorder these layers were removed from the sequence and the gaps that were produced along the profiles by the removal were closed obtaining a shortened depth radiocarbon age estimates from these cores and from earlier studies allow us to construct a paleosecular variation psv record for the past 24 000 years these results show good correlation with the previous one the spectrum obtained from spectral analysis shows major peaks at periodicities of about 1150 1500 2490 3630 5240 and 11 810 years both clockwise and counterclockwise precession of the geomagnetic vector is evident from analysis of the bauer plots with a preponderance of clockwise movement

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

evidence supporting holocene loess in illinois with new proxy data and historical regional perspectives on loess deposition in the upper mississippi river valley abstract we thank grimley et al 2019 for their constructive comments on our publication on holocene loess in illinois revealed by optically stimulated luminescence osl dating miao et al 2018 in the journal quaternary science reviews their skepticism on the preservation of holocene loess in illinois provides us with a good opportunity to clarify several key issues pedoturbation including bioturbation the methodology of soil research and our osl dating results in addition we will discuss the more fundamental issue behind this debate what controls loess deposition in the midwestern usa direct glacial sediment supply or broader scale climate change finally we also report new high resolution grain size magnetic susceptibility and color data from one of our holocene loess sites

reconstruction of hydrological changes and response to effective moisture variations from north central usa lake sediments abstract ratios of the stable isotopes of oxygen and carbon in benthic ostracodes and marl from cores taken from two lakes in north central minnesota reflect holocene hydrological and vegetation changes oxygen isotopes show that williams and shingobee lakes located in the same watershed but with different positions along a hydrologic gradient were connected before 9 8 ka as part of a larger lake lake willobee from 9 8 7 7 ka the level of lake willobee fell as a result of glacial retreat and increasing evaporation leaving small separated basins further decreases in lake level after 7 7 ka due to increasing aridity triggered the inflow of ground water in williams lake at about 7 ka and in shingobee lake at about 5 ka after 4 ka effective moisture increased the carbon isotope record reflects changes in vegetation with higher 13 c values during the prairie period 7 7 4 ka and lower values during preceding and succeeding forest periods the differences in timing of hydrological events show that the biotic and geochemical response of the lakes to climate variations is mediated by their hydrologic systems the response may be strongly spatially heterogeneous and can result in contrasting information from geochemical and biotic proxies from the same paleorecord

comparison of modern and ancient vertisols developed on limestone in terms of their geochemistry and parent material identification of paleosol parent material can be difficult a common simplistic assumption is that nonpedogenic strata directly beneath paleosols are representative of the parent material field relationships petrography and geochemical massbalance were used to test the simple hypothesis that the parent material of both an early carboniferous late mississippian vertic vertisol like paleosol and a modern analog soil vertisol was immediately subjacent marine carbonate rock an alternative hypothesis also tested was that the paleosol formed primarily from siliciclastic sediment deposited on top of the carbonate the modern ancient analog comparison is valid because both the paleosol and the modern soil have high clay contents extensive shrink swell features and rest directly on top of marine carbonate substrates field and thin section observations indicate minor assimilation of marine carbonate into both the paleosol and soil matrices mass balance of both the paleosol and soil calculated assuming that the subjacent carbonate was the parent material and that ti was immobile during weathering indicated 25 75 net volume loss during weathering and 25 99 net losses of many alkali alkaline earth and redox sensitive elements however calculations based on an alternative hypothesis of clayshale parent material for the paleosol indicated only 10 25 volume loss and lower translocation losses for weathering of this material the insoluble residue content of the dolostone would require that a fourfold volume reduction during weathering occurred if the dolostone were the only parent material if the paleosol formed from clayshale then significantly less volume loss characterised weathering these results collectively illustrate that the simplest interpretation of paleosol parent material may not always be correct and that paleosols can be derived from weathering of more than one parent material d 2002 elsevier science b v all rights reserved

some new aspects for the modelling of isothermal remanent magnetization acquisition curves by cumulative log gaussian functions rock samples containing ferri magnetic minerals acquire an isothermal remanent magnetization irm after exposure to a direct magnetic field measuring irm b allows to produce irm acquisition curves which were modelled by cumulative log gaussian clg functions robertson and france 1994 to discriminate the different magnetic phases an approach of how to find the best model has been added to this method from the investigation of a magnetite sample it is inferred that with the method the remanence acquisition coercive force for each magnetic component in a sample can be deduced the method allows to detect minute concentrations of magnetically hard material in a predominant magnetically soft sample and vice versa it furthermore allows to extrapolate the irm behaviour of samples that do not reach saturation irm in the experiment the study of a natural hematite renders it possible that even well defined hematite may be contaminated by ferri magnetic impurities biasing the remanence acquisition coercive force of the sample towards lower values

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

palaeomagnetic secular variation and rock magnetic studies of holocene sediments from a maar lake hoya de san nicolas in central mexico summary three up to 520 cm long sediment cores from hoya san nicolas in guanajuato mexico were analysed for various magnetic properties in order to better define a palaeomagnetic secular curve for central mexico the results magnetic susceptibility hysteresis cycles anhysteretic and isothermal remanent magnetization suggest that the remanent magnetization of the sediments is controlled by ferrimagnetic minerals pseudo single domain magnetite which are suitable recorders of the geomagnetic field the age depth model indicates average deposition rates of 0 32 interval 146 198 cm and 0 45 mm yr 1 interval 200 520 cm and a basal age of about 11 600 calibrated years bp cal yr bp we used magnetic susceptibility and natural remanent magnetization to correlate the three cores a composite palaeomagnetic secular variation sv record was obtained from the cores with a stretching and stacking process and a chronology established with accelerator mass spectrometer dates on microscopic charcoal and stratigraphic correlations with other well dated holocene records from mexico and guatemala the declination and inclination results show oscillatory behaviour varying in a narrow range although a distinctive directional swing is evident between 9060 and 9810 cal yr bp the san nicolas palaeomagnetic sv curve is similar to palaeomagnetic master curves from europe and north america in shape occurrence and synchronicity of directional features especially with respect to inclination

secular variation in mexico during the last 40 000 years paleomagnetic data are available for mexico from various archives covering irregularly the last 40 000 years data obtained from lake sediments are affected by ambiguous conversion of age to depth and the paleomagnetic data themselves are not of high quality as samples were only demagnetized at one field intensity these lake sediment data are therefore considered as less reliable for construction of a secular variation curve although they may give some qualitative information for the last 25 000 years archeological samples provide data for the period 100 1200 a d their 14 c ages are some times not well constrained with unrecoverable analytical and statistical procedures and often ages were only inferred from the stratigraphic position and the paleomagnetic record the paleomagnetic record of these materials is of high quality with very low internal dispersion although no magnetic cleaning techniques have been applied variations of inclination and declination with time are hampered by large age uncertainties and thus of limited value for the construction of secular variation curves paleomagnetic data from an u th dated stalagmite provide reasonable directions for most of the last 1200 years being of lower quality in those parts with very low remanence intensity the u th age determinations were interpreted in terms of a constant growth rate which might be only valid as a first order approximation recent volcanic rocks from the trans mexican volcanic belt provide 19 paleomagnetic directions of reasonable to high quality and often also absolute paleointensities ages have been determined from 14 c analysis of charcoal or paleosols found below the lavas and extend over the last 40 000 years therefore volcanic rocks provide the most adequate archive for the construction of a secular variation curve but much more volcanic structures need to be dated to obtain a semi continuous secular variation curve comparison of the data from different archives is possible mainly for the last 2500 years and despite the aforementioned problems similar variations of declination and inclination are observed this holds as well when comparing them to data from holocene volcanic rocks from western north america 2002 elsevier science b v all rights reserved

episodic deposition of illinois valley peoria silt in association with lake michigan lobe fluctuations during the last glacial maximum the chronology and cause of millennial depositional oscillations within last glacial loess of the central lowlands of the united states are uncertain here we present a new age model that indicates the peoria silt along the illinois river valley accumulated episodically from 28 500 to 16 000 cal yr bp as the lake michigan lobe margin fluctuated within northeastern illinois the age model indicates accelerated loess deposition coincident with regional glacial advances during the local last glacial maximum a weakly developed paleosol the jules geosol represents a period of significantly slower deposition from 23 700 to 22 000 cal yr bp a gastropod assemblage based reconstruction of mean july temperature shows temperatures 6 10 c cooler than modern during peoria silt deposition stable oxygen and carbon isotope values 18 o and 13 c of gastropod carbonate do not vary significantly across the pedostratigraphic boundary of the jules geosol suggesting slower loess accumulation was a result of reduced glacial sediment supply rather than direct climatic factors however a decrease in 18 o values occurred between 26 000 and 24 000 cal yr bp synchronous with the lake michigan lobe s southernmost advance this 18 o decrease suggests a coupling of regional summer hydroclimate and ice lobe position during the late glacial period

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

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

late quaternary aeolian and fluvial aeolian deposits from southwestern pampas of argentina southern south america abstract the central region of argentina southern south america is characterized by an extensive quaternary aeolian record in this context three locations from the southwestern pampas an andean foreland region bearing a rich fossil mammal record that contributed to the south america biostratigraphic scheme were selected to carry out a comprehensive sedimentological analysis of the late quaternary deposits the case studies are located at the transverse valleys of la pampa province chapalco quehue and utracan argentino valleys and exhibit a high resolution of the late quaternary in comparison with others areas of the southwestern pampas the toay locality 36 41 s 64 24 w records aeolian dominant activity since the end of the late pleistocene 30 ka onwards soil formation at some point during the holocene and early mid 20th century reactivation of aeolian process the arroyo quehue locality 37 04 s 64 42 w presents a late pleistocene holocene succession mostly related to an ephemeral endorheic fluvial system with an interval of relative surface stabilization and aeolian aggradation during the late holocene the utracan locality 37 17 s 64 35 w exhibits a prevailing aeolian and fluvial aeolian interaction succession developed in the mid to late holocene in a sand mud flat environment of a shallow saline lake the three studied cases are representative of aeolian aggradation in association with ephemeral fluvial shallow lake and pedogenic processes in a currently subhumid dry region numerical ages indicate sedimentation during the last 30 kyr they allow constraining and evaluating the paleoenvironmental conditions in this inland region of southern south america and provide age constraints for the regional databases of paleoclimatic proxies the results are in agreement with other late quaternary paleoclimatic paleoenvironmental archives of central argentina and show a fragile aeolian landscape that is susceptible to deterioration under extreme conditions including both aeolian reactivation during dry phases and erosion of sandy silty sediments during wet phases

testing the fidelity of sediment chronology comparison of varve and paleomagnetic results from holocene lake sediments from central finland abstract a careful construction of independent varve and paleomagnetic chronologies from three varved lake sediment records from central finland resulted in detailed and continuous age depth profiles cumulative varve calculation errors were estimated to be 3 for lake alimmainen savijarvi 10 295 340 varve years and 1 for lakes nautajarvi 9898 97 varve years and korttajarvi 9590 103 varve years paleomagnetic secular variation psv curves demonstrate good consistency between these sites and within a margin of varve chronology error they show similar declination and inclination features commonly described in the uk and sweden the timing of psv patterns from finnish varved sites agree well with uk curves between the present and 2000 bc and in pre 6000 bc deposits and with swedish data between the present and 5000 bc combined inclination records from three independently dated finnish varved sites possess an opportunity for accurate paleomagnetic comparisons within the margin of varve chronology errors and throughout the last 10 000 years

timing and origin for sand dunes in the green river lowland of illinois upper mississippi river valley usa abstract the recent increase in dune studies in north america has been heavily focused in the great plains while less attention has historically been given to the dune fields east of the mississippi river here we report ages and suggest a potential sediment source for sand dunes in the green river lowland illinois which may provide a better understanding of the dynamic interactions between eolian glacial lacustrine and fluvial processes that shaped the landscapes of the upper midwest seven coherent optically stimulated luminescence ages osl or optical ages obtained from four sites suggest that major dune construction in the green river lowland occurred within a narrow time window around 17 500 ago this implies either an enhanced aridity or an episodic increase of sediment supply at 17 500 years ago or combination of the both contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the lake michigan lobe retreated from the area we propose that green river lowland dunes sand originated from the green bay lobe through the rock river specifically sediment supply increased in the rock river valley during drainage of glacial lake scuppernong which formed between 18 000 and 17 000 years ago when the green bay lobe retreated from its terminal moraine the lake drained catastrophically through the rock river valley providing glacial sediment and water to erode the preexisting sandy sediments throughout the remainder of the late pleistocene the laurentide ice sheet drained into larger more northerly glacial lakes that in turn drained through other river valleys therefore the dunes in the green river lowland formed only during the catastrophic drainage of glacial lake scuppernong but were stabilized through the remainder of the pleistocene this scenario explains the abrupt dune construction around 17 500 years ago and explains the lack of later dune activity up to the pleistocene holocene transition osl and radiocarbon ages also indicate that dunes were reactivated during the early middle and late holocene some eolian activation occurred within well defined dry intervals in the upper midwest suggesting that increased aridity may have been the primary driver in mobilizing sand however many ages do not correspond to drier periods in contrast to the relative coherency of the pleistocene osl ages from multiple study sites the holocene osl ages do not overlap from one site to another suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation in the holocene therefore we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the holocene the multiple periods of eolian activity during the holocene suggest a high potential for future sand activation in the region and these results are informative for environmental prediction and potential future mitigation

the importance of both geological and pedological processes in control of grain size and sedimentation rates in peoria loess abstract the loess paleosol succession in the peoria loess in southern illinois is characterized as alternating loess layers and weathering bands known as paleosol a horizons the fast loess accumulation during the late wisconsin glaciation interacted with the incipient pedogenesis and caused unclear boundaries of loess paleosol alternations in soil horizonation and mineralogy parameters of grain size distribution sedimentation rate matrix carbonate content and diffuse reflectance i e soil colors and iron oxides are used in this paper to discuss the geological and pedological influences for the peoria loess in keller farm section in southern illinois the multi proxy analysis revealed that many paleosol a horizons defined by the diffuse reflectance variability contain finer grained materials with a relatively higher sedimentation rate it suggests that glaciofluvial sediments were available in the source areas for uploading eolian dust during the temporary ice sheet retreats the denser vegetation and wetter surface soils on the loess deposit area could increase the dust trapping efficiency and caused a greater accumulation rate of loess deposits the coarser grained materials and slower sedimentation rate are often found in loess layers it suggests that strong surface winds transported the coarser grained materials from local dust sources and sparse vegetation and dry surface soils reduced the dust trapping efficiency during the ice sheet readvance the strong interactions between the geological and pedological processes played an important role on the loess paleosol alternations in southern illinois during the late wisconsin glaciation

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

soil geomorphic relations of lamellae in eolian sand on the high plains of texas and new mexico clay lamellae are ubiquitous features in sands in a wide variety of settings around the world most studies of lamellae focus on 1 a few or individual locales or on 2 formation by experimental methods in the laboratory this study reports on lamellae from eight localities in three late quaternary dune fields on the southern high plains of northwest texas and eastern new mexico most lamellae observed are illuvial and they increase in number and thickness through time a few 1 3 thin 1 2 mm lamellae formed in historic sediments lamellae are more numerous 3 12 and thicker 3 5 mm in older late holocene b 1000 14 c years bp and middle holocene b 7600 14 c years bp sands soils that formed through the late pleistocene and into the early holocene 14 300 7600 14 c years bp or soils that formed throughout the holocene can exhibit as many as 30 lamellae or lamellae of 10 12 mm thickness the micromorphology of the lamellae shows that argillans on sand grains are thicker more laminated more continuous and cap and link more grains through time other variables affect lamella morphology within individual dunes the lamellae are best expressed where the sand is thickest they decrease in number and thickness as sand thins the lamellae also form only in clean well drained sand poor drainage and or bioturbation result in formation of a continuous argillic horizon encasing lamellae d 2005 elsevier b v all rights reserved

sedimentary aggregates in the peoria loess of nebraska usa loess grain size data used to infer transport direction or wind strength are generally derived from vigorously disaggregated samples however these data may not adequately represent the effective particle size distribution during loess transport if the transported dust contained aggregates of finegrained material thin sections of minimally altered c and bc horizons in the late pleistocene peoria loess of nebraska usa indicate the presence of aggregates with diameters of 30 1000 am the larger aggregates 250 am are unlikely to have been transported and are interpreted as the result of soil faunal activity and other pedogenic processes after deposition aggregates smaller than 250 am could have a similar origin but laser diffraction particle size analysis suggests that many are sedimentary particles comparison of minimally and fully dispersed particle size distributions from each sampling site was used to estimate the modal diameter of aggregates the aggregate modal diameter becomes finer with decreasing loess thickness representing increasing distance from the source a similar trend was observed in the modal diameter of fully dispersed particle size distributions which represents the mode of sand and silt transported as individual grains we interpret both trends as the result of sorting during transport supporting the interpretation that many of the aggregates were transported rather than formed in place aggregate content appears to increase with distance from the source explaining a much more rapid downwind increase in clay content than would be expected if clay were transported as particles smaller than 2 am diameter although the peoria loess of nebraska contains sedimentary aggregates many of the coarse silt and sand grains in

construction of type curves of geomagnetic secular variation for dating lake sediments from east central north america type curves of palaeomagnetic secular variations of declination and inclination through the last 12 000 radiocarbon years have been constructed by combining data from the minnesota lakes with paral

aeolian silt contribution to soils on mountain slopes mt śleza southwest poland this paper evaluates the possible contribution of aeolian silt to soils of mt leza southwest poland silt loam textures are common across lower silesia and are often confused with silt clay loam especially at the outer boundaries with thin loess deposits eight study sites with different thicknesses of silt loam mantles that are covered and or mixed with underlying sediments were examined in the field to test our hypothesis we analyzed the particle size and geochemistry of representative horizons concentrations of major and trace elements as well as their cross ratios confirmed the aeolian origin of silt loam materials and clearly distinguished them from basal sediments there is a clear relationship between the presence and depth of aeolian mantles and mixing zones with the type of underlying material furthermore the incorporation of aeolian silt to regoliths soils was a main agent initiating and stimulating clay translocation leading to the formation of an argic horizon below the silt mantles mixing aeolian silt with acid granite regoliths and further illuviation resulted in the formation of alisols while silt contributions to serpentine sediments resulted in development of skeletic luvisols soils receiving very weak input of aeolian silts remain as leptosols cambisols

a palaeomagnetic secular variation record from late pleistocene holocene lacustrine sediments from chalco lake basin of mexico palaeomagnetic secular variation is reported for the past 25 000 years from the lacustrine sequence of chalco lake basin of mexico the rock magnetic and palaeodirectional record is obtained from a 11 27 m core drilled in the central sector of the lake 19 25 n 99 w detailed stratigraphy pollen and diatom studies provide a reconstruction of the environmental evolution the depth time scale transformation is derived from nine 14c dates which give depositional rates of 0 28 mm year for the first 3 5 m and 0 80 mm year between 3 5 m and 11 27 m spectral analysis of intensity and directional records shows low frequency components with characteristic periods of 10 500 3200 3400 2900 3000 1400 1500 and 800 900 years in phase oscillations of inclination and intensity records point to drifting non dipole field anomalies mean inclination anomaly is 2 4 which is similar to results from volcanic rocks of the basin of mexico and hawaii and which support a zonal character of the non dipole field the palaeomagnetic vectors describe characteristic loops with dominant clockwise sense in the intervals 2000 5600 12 000 15 000 and 18 600 24 000 years and dominant counterclockwise sense in the intervals from 6500 to 11 000 and 16 600 18 500 years clockwise vector rotation may represent westward drift of non dipole field anomalies though westward drift may also result in counterclockwise vector motion major declination swings are related to environmental and depositional disturbances and without further confirmation they cannot be considered as geomagnetic variations