Distribution Of Loess Research Articles

Analysis on Collapsibility and Microstructure of Unsaturated Loess Using Fractal Geometry

This paper studies the microstructure of 16 group samples from three different sites of North-west region in P. R. China. Pictures of microstructure were processed with imaging processing program to acquire the geometer parameter and fractal dimension of pores. The range of pores’ fractal dimension is between 1.816~1.936. The pore distribution function of unsaturated soil is established based on fractal geometry theory. The pore water distribution of loess under natural moisture is analyzed. The relationships of collapsibility coefficient with fractal dimension and porosity of unsaturated pores are analyzed with the method of regression analysis. A larger fractal dimension represents a more complex pore-structure. The collapsibility coefficient of loess increases with the increase of fractal dimension and porosity of unsaturated pores.

Loess distribution on the northern flank of Ligurian Alps (NW-Italy): topographic influences and paleoenviromental implications

Loess distribution on the northern flank of Ligurian Alps (NW-Italy): topographic influences and paleoenviromental implications

Sensitivity of frost weathering and aeolian deposition during genesis of Late Quaternary periglacial slope covers on calcareous rocks of a Muschelkalk landscape, eastern Thuringian Basin, Germany

Pleistocene, periglacial loose rock covers on calcareous rocks of Mesozoic Muschelkalk contain sediments, which are derived from loess deposition, frost weathering as well as limestone dissolution processes. Distinct sediments form periglacial slope deposits (PSD) with a layered vertical structure, consisting of Basal Layers (BL), Intermediate Layers (IL) and Upper Layer (UL). The Basal Layer has in part a notably more complex structure than on siliceous or quartz bedrock. The lithological and petrological properties of calcareous rock types are reflected by remarkably different structure, thickness and clast properties of frost shattered debris within the investigated Muschelkalk landscape as well as in chemical weathering rates within the debris. Furthermore, we could detect a high variability in the thickness and distribution of aeolian matter, too. We assume that the deposition of loess sediments might be sensitive to both properties and patterns of debris cover and to the amount of pre-existing “Braunlehm” that resulted from limestone dissolution processes. Soil moisture conditions and vegetation cover might have been as crucial factors for loess distribution as luff-/lee-effects of the regional wind system or karst surface morphology. Considering the ecological consequences implied by the structure and heterogeneity of periglacial loose rock cover, limestone landscapes in general seem to be vulnerable to degradation processes. Particularly sites of shallow sediment depth or rich in rock debris might be rapidly degraded by soil erosion, have low protection potential against groundwater pollution and might have a high sensitivity towards climatic impacts like water shortage and drought stress.

Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range, Germany: A Laboratory and Field Study

Field and laboratory investigations were performed to identify the principal mechanisms of the hydrochemical groundwater evolution among low mineralised groundwater in the Triassic Bunter sandstone aquifer of the Odenwald low mountain range, central Germany. Hydrochemical composition comprises low pH, SO4-rich shallow groundwaters issued by springs (Ca-Mg-SO4-type) grading to SO4-poor deep groundwaters with near-neutral pH (Ca-HCO3-type). Batch experiments of the original rock were run to determine primary mineral alteration reactions and the origin of dissolved ions. Principal experimental reactions comprise the decomposition of anorthite, K-feldspar, biotite and jarosite as mineral components of the original sandstone rock and the formation of clay minerals of the smectite group (Ca-montmorillonite, beidellite), and iron hydroxides as secondary minerals. Mobilisation of fluid inclusion in quartz grains contributes to Na and Cl concentrations in the leachates. The evolution of deep groundwater circulation proceeds by mineral alteration reactions calculated by the inverse modelling of both primary and secondary minerals to produce low-T mineral phases. The dissolution of K-feldspar converts Ca-montmorillonite to illite (illitisation). The formation of Na-beidellite correlates with decreasing concentration of Na in solution. Mineral reactions further proceed to the formation of kaolinite as stable mineral phase. As indicated by modelled adsorption curves, the decrease of SO4 concentrations during groundwater evolution relates to the adsorption of SO4 on iron hydroxides. The leaching of calcite indicated for individual groundwaters relates to the distribution of loess in the appropriate catchment areas.

Loess of the Lizard Peninsula, Cornwall, SW Britain

The geology of the Lizard Peninsula, the UK’s most southerly projection into the English Channel, is dominated by serpentinised peridotites, gabbro and amphibolites of the Palaeozoic Lizard Complex. Its Cainozoic history dates to at least the Palaeogene, resulting in a relatively complete record of events, involving the deposition of the anomalous quartzose Crousa gravels, intense weathering, possible fault controlled uplift, development of the current drainage pattern, subsequent coastal modification by marine erosion prior to the deposition of presumed Mid to Late Pleistocene raised beaches, soliflucted diamicts, and Late Pleistocene loess. The Lizard Loess, a UK lithostratigraphic formation, is generally perceived as a thin deposit extensively developed inland and capping the thicker diamict/‘head’ sequences on the coast. This study indicates that these sequences (coastal ‘head’ units) are themselves loessic on the serpentinised peridotite and amphibolite coasts and gabbroic headlands. The location and distribution of loess on the peninsula have been influenced by its rock types and their local weathering/erosion regime. There appears to have an earlier phase of Late Pleistocene loess deposition, associated with dynamic periglacial processes, contemporaneous with other ‘head’ deposits both on the Lizard and elsewhere in south Cornwall. A later widely preserved phase with more quiescent conditions followed. The currently accepted (15.9 ka) age for the Lizard loess almost certainly belongs to this later phase.

Franz Ritter von Hauer’s work and one of the first loess map of Central Europe

Franz Ritter von Hauer was the second Director of the Geological Survey in Vienna (1866–1885). The primary research of von Hauer was devoted chiefly to the evolutionary history of Cephalopods and geological mapping. Among several investigations of Cephalopods of the Triassic and Jurassic formations of the Alpine regions, he recognized and discovered 89 species and established the Middle and Late Triassic stratigraphical units of deep shelf environments: the Hallstadt facies. One of his main contributions to Quaternary science was the geology textbook of the former Austro-Hungarian Monarchy, which provided a resource to access recent developments in geology and notably loess research to many scientists. Besides the staff from the Geological Survey, von Hauer involved numerous local, well recognized experts and organized regional centres for geological investigations. This well managed and effective work resulted in a great number of publications, many of which were the reports published by the Geological Survey. The General Geological Map of the Austro-Hungarian Monarchy was one of the most comprehensive and complete geological map of Central Europe during that period of time. It was presented in Cologne (1865) and from 1867 until 1884 ran to four editions. The Quaternary formations were presented in two groups: Pleistocene and Holocene formations. The Pleistocene formations identified as “Dilluvial” formations and were represented predominantly as gravels and sand and also as loess. The Holocene formations were described as “Alluvial” formations. They were mapped as: peat, lime tuff, quicksand and other formations named only as “Alluvial formations”. Loess was mentioned exclusively as a Pleistocene (“Dilluvial”) formation. The distribution of loess was clearly outlined. Due to the development of the science at that time, the term loess was not clearly defined and as such at some places, loess-like sediments such as colluvial were also mapped as loess. Nevertheless it was one of the first maps which documented the extent of loess deposits and including the regions of Lower Austria with Vienna Basin, Bohemia and Moravia, the Carpathian Basin, parts of the Polish Lowland and Transylvania.

Late Quaternary loess landscape evolution on an active tectonic margin, Charwell Basin, South Island, New Zealand

Loess deposits constitute an important archive of aeolian deposition reflecting wider patterns of glacial atmospheric circulation, and more localised interactions between riverine source areas, loess trapping efficiency and geomorphic controls on erosion rate. Conceptual models have been formulated to explain the coeval evolution of loess mantles and associated landscapes (loess landscape models) but none apply to areas of tectonically induced base-level lowering. This study uses an age sequence of alluvial fill terraces in the Charwell Basin, north-eastern South Island New Zealand, which straddles the transpressive Hope Fault, to investigate geomorphic controls on loess landscape evolution in an active tectonic region. We hypothesize that the more evolved drainage networks on older terraces will more effectively propagate base-level lowering by way of a greater areal proportion of steep and convex hillslopes and a smaller proportion of non-eroding interfluves. Eventually, as the proportion of interfluves diminishes and hillslope convexity increases, terraces shift from being net loess accumulators to areas of net loess erosion. We investigate the nature of erosion and the geomorphic thresholds associated with this transition. Morphometric analysis of alluvial terraces and terrace remnants of increasing age demonstrated geomorphic evolution through time, with a decrease in extent of original planar terrace tread morphology and an increase in frequency of steeper slopes and convexo-concave land elements. The number of loess sheets and the thickness of loess increased across the three youngest terraces. The next oldest (ca. 150 ka) terrace remnant had the greatest maximum number of loess sheets (3) and loess thickness (8 m) but the loess mantle was highly variable. A detailed loess stratigraphic analysis and the morphometric analysis place this terrace in a transition between dominantly planar, uniformly loess-mantled landforms and loess-free ridge and valley terrain exemplified by the oldest terrace remnant. Variations in thickness and preservation of loess sheets demonstrated spatially and temporally variable erosion during loess accumulation. To test our hypothesis of loess persistence we calculated critical steady-state hillslope curvatures from a soil transport model, calibrated for the study area, above which the uppermost loess sheet (L1, max. thickness 1.8 m) should be completely eroded. We compared loess distribution mapped in the field to values of slope curvature calculated from topographic surveys and found two of three critical curvature values had acceptable predictive ability. Where predictions failed this is probably due to transient responses related to active steam incision. Because all critical curvature values predicted presence of loess on the oldest terrace remnant where there is none we conclude that important factors other than morphometric ones are important in determining loess distribution in loess landscapes in active tectonic regions. These may include internal changes to regolith affecting erodibility, or vegetation or topographic interaction with wind patterns affecting loess trapping.

Reconstruction of Quaternary landscape formation as a tool to understand present geomorphological processes in the eastern Prealps (Austria)

The Rhenodanubian Flysch of the N Vienna Forest is composed of various layers of sandstones, marly shales, calcareous marls and clay schists, covered by Quaternary periglacial cover beds and loess deposits. There is a characteristic sequence of slope evolution during the Quaternary. Seven main phases are related to Pleistocene processes and two stages reflect the most recent geomorphodynamic processes. Phases of erosion, redeposition, sedimentation, and soil formation demonstrate stages of activity and stability under varying climatic conditions. On the basis of pedological and geomorphological investigations, it is possible to differentiate Pleistocene and Holocene sediments and processes. In particular, the distribution of periglacial cover beds, loess and modern soils allows the reconstruction of the undisturbed Pleistocene slope and sediments. The sequence of slope formation causes a distinct spatial distribution of Quaternary sediments and solid rock at the present land surface. In consequence, the influence of Quaternary landscape formation significantly influences slope stability conditions in the study area. This applies to the specific composition of the basal periglacial cover bed in the study area. It often consists of densely bedded marls and sandstone and is therefore impermeable, which can induce mass movements in the study area. Loess deposits frequently slide on top of the basal periglacial cover bed and form a susceptible pre-requisite for the occurrence of landslides in the study area.

Significance of primary hilltop loess in reconstructing dust chronology, accretion rates, and sources: An example from the Negev Desert, Israel

Although high‐latitude loess sequences have been studied extensively for reconstructing past climates, loess in desert margins has been mostly overlooked. Moreover, many low‐latitude loess studies have focused on secondary, reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control. In this respect, the spatial distribution of the loess and its different types are crucial. In this study, we differentiate primary and secondary loess using remote sensing and field criteria. We present remote sensing and geographic information system procedures for mapping loess distribution, in general, and for identifying pristine hilltop loess sequences in particular. Then, we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary, hilltop loess sequence in the Negev desert that show that the late Pleistocene Negev loess started accumulating at ∼95 ka, much earlier than previously proposed (∼70 ka). It was preceded by a previously unknown middle Pleistocene period of loess formation at ∼180–130 ka. The ages also suggest that the threshold of dust accretion rate needed for loess formation is ∼0.02 mm a−1 (∼30 g m−2 a−1), a factor of 2 or more lower than previously thought (0.04 to 1.0 mm a−1). Our results also provide insights into causes of late Pleistocene loess accretion and its close association with regional dune field activity. The methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other, more remote desert areas.

Automatic landform stratification and environmental correlation for modelling loess landscapes in North Otago, South Island, New Zealand

The advent of quantitative soil-landscape modelling techniques has seen the mapping of pedological phenomena placed on a more scientific footing. In New Zealand, the spatial distribution of loess has a significant influence on soil properties, and recent regional-scale quantitative models have attempted to model the thickness and pattern of this important soil parent material. Here we apply two quantitative modelling techniques, automatic landform stratification and environmental correlation, to test and refine loess-landscape models for a higher-resolution study window in North Otago, South Island. Field validation demonstrated that previously developed coarse-scale models were moderately successful in predicting loess thickness, but these models required refinement. Automatic landform stratification based on conceptual models of loess distribution was a good predictor of primary loess in the field (85% success), but predicted poorly occurrence of colluvial and thin loess. Environmental correlation using nominal logistic regression with equal prior probabilities was a good predictor of primary loess in the field (70% success), but predicted poorly occurrence of colluvial and thin loess. Quantitative loess-landscape models need to be further refined using higher-resolution terrain data derived from LIDAR and photogrammetric surveys. In addition, morphometric similarities between different loess landscapes needs to be addressed and the historical and spatial contingency inherent in loess-landscape evolution incorporated in models for improved spatial prediction of loess parent materials.

The Matuyama/Brunhes boundary in loess sections in the south of the East European Plain and their correlation on the basis of palaeomagnetic and palaeopedologic data

The Matuyama/Brunhes boundary (MBB) in loess sections of the East European Plain, one of the greatest areas of global loess distribution, is a highly debatable issue. The ambiguity of the MBB position here results from the complexity of loess/soil magnetization processes and an apparent delay in loess remanence acquisition, and from the uncertainties of pedostratigraphic interpretations. In the Don Glaciation area, the MBB is unanimously placed below the Don moraine, although the exact position is still controversial. In the sites of the Northern Azov Sea, the MBB is, however, placed in the loess horizon considered to be the equivalent of the Don moraine in the north. The inconsistency of this interpretation is demonstrated by detailed magnetostratigraphic and pedostratigraphic studies in the western sites of Zaporozh'e (Dnieper basin), Novaya Etuliya (Lower Danube basin) and Roxolany (Lower Dniester basin). In all these sites, albeit with certain minor discrepancies, the MBB is found two or three interglacial palaeosols below the Don loess, which is overlain by the good stratigraphic marker of the Vorona pedocomplex, a thick polygenetic red-brown palaeosol formed supposedly in a Mediterranean climate. Here the MBB is placed in a ‘quadruple soil’ unit, termed “Roxolany loess/soil suite”, which consists of four closely spaced, strongly calcareous soils occupying an interval between the Don loess on top and the earlier well-developed Bobrov (?) loess with reversed Matuyama magnetization. The Roxolany suite can possibly be correlated with the three palaeosols of the pre-Don Ilyinka unit of the Russian Unified Stratigraphic Scheme and thus confirms the interpretation of the MBB in the central areas of the East European Plain as to the interval between the Ternovka (second-pre-Don) palaeosol and the Troitsk (third pre-Don) palaeosol.

Rivers and loess: The significance of long river transportation in the complex event-sequence approach to loess deposit formation

Rivers are essential for loess deposit formation. River systems which relate directly to loess deposit formation include the Danube and the Rhine; the Mississippi and the Missouri; the Thames and the Medway; the Indus, Ganges and Brahmaputra; the Dnepr, Don and Volga; the Clutha, Mataura and Rakaia—New Zealand rivers; the Yellow River; rivers in South America; Siberian rivers (flowing north); the Odra and the Wisla (between the mountains and the ice); the Syr-Darya and Amu-Darya (into the desert). The contention is that rivers are not just important in major loess deposit formation, they are mandatory (necessary, imperative, obligatory, essential, indispensable, requisite). For a complete and satisfactory study of a loess deposit, we need to know how the material is produced; how it is transported and distributed across the landscape; how intermediate deposits are formed; how transportation provides the defining properties (i.e., open structure, collapsibility, draping across the landscape); and what may happen post-deposition (e.g., chernozemisation, fragipan formation, increased collapsibility, etc.). If rivers are essential then it would appear that the British loess is probably Alpine material delivered by the proto-Rhine and the Polish loess is not derived from the ice-sheet to the north but from the mountains to the south. The lack of loess in Canada is explained by the absence of suitable rivers. The loess in Russia and neighbouring countries can be classified (as Jefferson et al. [Jefferson, I.F., Evstatiev, D., Karastenev, D., Mavlyanova, N.G., Smalley, I.J., 2003b. The engineering geology of loess and loess-like deposits: a commentary on the Russian literature. Engineering Geology 68, 333–351] suggested) on the basis of associated rivers. A ‘new’ deposit of glacial loess is recognised—associated with the Dnepr, Don and Volga rivers (the USWR loess). The Smalley–Leach [Smalley, I.J., Leach, J.A., 1978. The origin and distribution of the loess in the Danube basin and associated regions of East-Central Europe: a review. Sedimentary Geology 21, 1–26. Available from: 〈 www.geo.edu.ro/sgr/mod/downloads/PDF/Smalley-SedGeo-1978.pdf〉] vision of the loess in the Danube basin and East-Central Europe is probably misconceived. They assigned a great significance to glacial action and put loess in a ‘northern band’. It appears that this proposed glacial influence is minimal and that the Danube loess is essentially mountain loess—derived from the Alps, the Carpathians, the Sudeten mountains and other high regions. The Danube system is a classic example of a river controlling loess distribution.

Evidence for an eolian origin for the silt-enriched soil mantles on the glaciated uplands of eastern Upper Michigan, USA

We provide textural, geochemical, and mineralogical data on a thin, silty deposit that unconformably mantles glaciated uplands in the eastern Upper Peninsula of Michigan. Previous research on this deposit, which we hypothesize to be loess, is nonexistent. The uplands were islands or narrow peninsulas within one or more glacial lakes. We compare the distribution, likely source and nature of the 20–60 cm thick silty mantle by using the loess formation model of Mason et al. [Mason, J.A., Nater, E.A., Zanner, C.W., Bell, J.C., 1999. A new model of topographic effects on the distribution of loess. Geomorphology 28, 223–236], which focuses on the generation of eolian silt by saltating sand across upwind, barren surfaces. Parabolic dunes, with arms open to the NW, are common on former lake floors upwind of the silt-mantled uplands, attesting to the strength and direction of paleowinds. The abrupt termination of the dunes at the footslopes of the uplands, associated with silt deposition on upland soil surfaces in downwind locations, are both consistent with the model of Mason et al. [Mason, J.A., Nater, E.A., Zanner, C.W., Bell, J.C., 1999. A new model of topographic effects on the distribution of loess. Geomorphology 28, 223−236]. Sediments on former lake floors contain abundant strata of fine/medium sand and silt, and thus are likely sources for the silt and dune sand. The cap, dune and lake sediments are similar along many different geochemical axes, whereas the substrate sediment, i.e., the drift below the cap, is unique. Cap sediments, normally containing roughly 30% silt, are enriched in quartz and depleted in Ti and Zr, relative to dune sediment. The dune sediment, a more residual eolian deposit, is enriched in Ti and Zr, relative to the cap, probably due to its greater abundance of heavy minerals. Therefore, we conclude that the silty cap is loess that was deflated from abandoned lake floors after nearby glacial lakes drained, probably contemporaneously with dune migration across the former lake floors.

Loess in Europe—its spatial distribution based on a European Loess Map, scale 1:2,500,000

The paper focuses on the concept, mapping and discussion of loess distribution in Western, Central and Eastern Europe at a scale of 1:2,500,000. The research work is based on studies and data compilation primarily carried out in the 1970s and 1980s [Fink, J., Haase, G., Ruske, R., 1977. Bemerkungen zur Lößkarte von Europe 1:2,5 Mio. Petermanns Geographische Mitteilungen 2(77), 81–94; Fink, J., 1969 Les progres de l’ etude de loess en Europe. Bulletin de l’ Association française pour l’ etude du Quarternaire 3–12. Haase, G., Ruske, R., Fink, J., 1983. Conception, preparation and some results of the Loess Map of Europe on a scale 1:2,5 Million. INQUA Newsletter 1983(1), 7–10] and completed recently by additional material and literature references. Reference is also made to recent GIS-based data processing and visualisation techniques that were utilised for the final version of the European Loess Map. The paper provides an overview of the history of the conceptualisation of the map as well as on the loess study in Europe, and than considers the cartographic data on loess sediment formation and distribution in Europe. The classification of loess and loess-like sediments and their distribution throughout Europe as reproduced in the map are discussed [Haase, G., Lieberoth, I., Ruske, R., 1970. Sedimente und Paläoböden im Lössgürtel. In: Richter, H., Haase, G., Lieberoth, I., Ruske, R. (Eds.), Periglazial-Löß-Paläolithikum om JUngpleistozän der Deutschen Demokratischen Republik; Petermanns Geographische Mitteilungen 274, 99–212]. The paper illustrates the final state of the loess distribution map of Europe at a scale of 1:2,500,000 and the digital data references on which it is based. Some applications of the map are suggested.

Modelling loess landscapes for the South Island, New Zealand, based on expert knowledge

In New Zealand, occurrence of loess often determines the spatial pattern of soil depth, and influences droughtiness, leaching potential, organic matter accumulation, nutrient retention, and natural plant‐species distribution. Understanding loess distribution is therefore a major prerequisite for soil and land resource management. Although New Zealand's soil scientists have accumulated a good empirical knowledge of loess distribution through several decades of field investigation, only some of this knowledge is recorded in papers and reports. This study estimates loess thickness and percent cover, and provides loess landscape models for the internal loess distribution of all land units in the South Island based on expert knowledge. We derived loess depth classes and percent cover classes and assembled land units with similar loess distribution patterns. The soil sets underpinning the map units of the New Zealand Land Resource Inventory (NZLRI) were classified according to loess depth, loess cover, and loess pattern. New loess maps of the South Island were produced from those classifications, displaying loess coverage, thickness, loess pattern, and loess landscapes. These maps present our current knowledge of the coarse‐scale loess distribution and provide a framework for fine‐scale loess landscape modelling.

Progress of loess research in China

Progress in Chinese loess research made in recent 15 years was introduced in this paper, including mainly distribution and paleoenvironment significance of Chinese loess, new development of loess formation age, red-brown paleosol types and environmental change, loess-paleosol sequence and climate cycles, monsoon strength change during last interglacial and last glacial periods in the Loess Plateau, climate events, and source areas of loess and material.

A combined modeling and measurement technique for estimating windblown dust emissions at Owens (dry) Lake, California

The problem of dust emissions from playa sources is an important one both in terms of human health and in terms of global dust issues, distribution of loess, and mineral cycling. A refined method of modeling atmospheric dust concentrations due to wind erosion was developed using real‐time saltation flux measurements and ambient dust monitoring data at Owens Lake, California. This modeling method may have practical applications for modeling the atmospheric effects of wind erosion in other areas. Windblown dust from the Owens Lake bed often causes violations of federal air quality standards for particulate matter (PM10) that are the highest levels measured in the United States. The goal of this study was to locate dust source areas on the exposed lake bed, estimate their PM10 emissions, and use air pollution modeling techniques to determine which areas caused or contributed to air quality violations. Previous research indicates that the vertical flux of PM10 (Fa) is generally proportional to the total horizontal saltation flux (q) for a given soil texture and surface condition. For this study, hourly PM10 emissions were estimated using Fa = K′ × m15, where m15 is the measured sand flux at 15 cm above the surface, and K′ was derived empirically by comparing air quality model predictions to monitored PM10 concentrations. Hourly sand flux was measured at 135 sites (1 km spacing) on the lake bed, and PM10 was monitored at six off‐lake sites for a 30 month period. K′ was found to change spatially and temporally over the sampling period. These changes appeared to be linked to different soil textures and to seasonal surface changes. K′ values compared favorably with other Fa/q values measured at Owens Lake using portable wind tunnel and micrometeorological methods. Hourly trends for the model‐predicted PM10 concentrations agreed well with monitored PM10 concentrations. Dust production was estimated at 7.2 × 104 t of PM10 for a 12 month period. A single storm accounted for 9% of the annual dust emissions at 6.5 × 103 t. The modeling results were used to identify 77 km2 of dust‐producing areas on the lake bed that will be controlled to attain the federal air quality standard for PM10.

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.

Genesis and distribution of the Late Pleistocene and Holocene loess of Argentina: a regional approximation

Abstract An overview of the current state of knowledge of the loess of Argentina is presented. The spatial distribution of the loess (typical or reworked) is described and, in particular, reference is made to the relationship between landforms and superficial materials in the sub-tropical loess region. The description of extrinsic and intrinsic characteristics demonstrates the influences of regional factors in loess distribution and the existence of a SW–NE loess transport path throughout Argentine territory. The available dating confirms the age of the superficial loess as Pleistocene and Holocene. It is pointed out that the temporal interval of deposition of the Late Pleistocene loess coincides with the highest dust concentrations as shown in the ice core records at both poles. The prominent influence of volcanic materials, affecting not only the mineral composition of the loess but also the genesis and evolution of the loess–palaeosol sequences, is emphasised. Finally, the importance of the palaeosols as indicators of palaeoenvironmental conditions is clearly demonstrated by the descriptions of outcrops in the pre-Andean valleys of north-western Argentina.

Geomorphic and pedogenic evidence for bioturbation of artifacts at a multicomponent site in Licking County, Ohio, U.S.A.

The distribution of artifacts at the multi-component (Paleoindian through Middle Woodland) Munson Springs site (33Li251) is best explained by downward migration of objects through bioturbation processes rather than by a vertical sequence of occupation surfaces through a period of sediment accretion. At the noncultivated, 1800 m2, footslope site, the distribution of glacial diamict, loess, and drift- and bedrock-derived colluvium indicate widespread slope erosion during the late-glacial period with general backslope and footslope stability during the Holocene. Diagnostic Paleoindian artifacts were recovered from a BE soil horizon lying directly below fill material of a small (8 × 10 m) Early Woodland mound. Based on soil fine clay distribution, these artifacts lay about 30 cm below the premound land surface. Woodland artifacts are concentrated at depths of 10–20 cm immediately down slope from the mound. Soil horizonation and total and fine clay distributions within footslope profiles indicate no significant sediment accretion through the period of soil genesis and prehistoric site occupation. © 2001 John Wiley & Sons, Inc.