The loess of West Europe

During the last thirthy years, many studies about loess and periglacial deposits have allowed to present a correlation table from the Netherlands and Belgium to north-west France. For the Quaternary, 11 main interglacial soils were recognized, separated during Early Pleistocene by combe-rock and solifluction deposits, and during Middle and Late Pleistocene by loess cycles. Two main loess basins exist in France. The most important is the Northern basin, continuing the sandy area of Belgium (cover sand) and the desert pavement of the Netherlands. The second is developed in Normandy and results from the Channel landscape open during pleniglacial periods. We have now stratigraphic tables at different time-scales. The main research axes must be now to attain a better knowledge about sources of loess materials, to estimate the volume of loess and its climatic significance and landscape variation during the pleniglacial events. Absolute datings of Middle Pleistocene stratigraphic details are needed to evaluate the differences between the different climatic cycles.     

Dust transport and the question of desert loess formation

Although contemporary dust storms are frequent in arid and semi-arid areas, desert loess deposits are poorly developed. Much of the World's loess occurs in mid-latitude areas which experienced glaciation during the Pleistocene. Ocean core evidence indicates that dust transport from sub-tropical deserts increased during cold stages of the Pleistocene, but loess formed only on certain desert margins, for reasons which have not been fully explained. This paper re-examines the mechanisms of dust transport and deposition, and the circumstances leading to the accumulation of thick loess. Typical loess is composed mainly of medium silt grains which are transported in short-term suspension a few metres above the ground. Significant thicknesses of loess form only when dust is trapped within a limited area, often relatively close to the source. Dust particles finer than 20 μm are transported mainly in long-term suspension over a greater height range and may be widely dispersed. The availability of silt and the frequency, magnitude and direction of dust-transporting winds are important factors governing the potential for loess formation, but the existence of a suitable dust trap is particularly important. Traps may be formed by topographic obstacles, areas of moist ground, or vegetated surfaces. Vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid-latitudes during the Pleistocene. Dust blown during glacial periods from certain deserts, notably in Sinai, Soviet Central Asia and China, accumulated as loess in neighbouring semi-arid regions. On the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps. During most of the Holocene net dust deposition rates in all desert-marginal areas have been too low for significant loess accumulation. This is mainly due to a reduction in silt availability and a tendency towards landscape stability. Reported dust storm frequencies during the past 50 years over-estimate the longer-term Holocene dust flux due to the effects of human activities. Much modern dust owes its origin to erosion of cultivated soils in semi-arid areas and is finer than typical loess.     

Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev Desert, Israel

Grain size analyses of three hilltop, primary eolian loess sequences in the Negev desert, southern Israel, show a bimodal grain-size distribution at 50-60 μm and 3-8 μm. Using analyses of mineralogy and OSL ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time, suggesting an enhancement of a time-transgressive proximal dust source compared to a distal, Saharan fine-grain dust. The only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into Sinai and the Negev concurrently with the loess accretion during the late Pleistocene as a result of the exposure of the Mediterranean shelf. We therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea. This relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as Northern Africa, China and Australia.     

Metamorphic feldspathization of metavolcanics and granitoids,Avnik area,Turkey

In the Avnik area of the Bingöl massif the Lower Unit consists of basic to felsic metavolcanics (ca. 450 Ma), intruded by granitoids (ca. 350 Ma). These are unconformably overlain by an Upper Unit of micaschists and Permian marbles; both units have been deformed and metamorphosed in Alpine time. The metavolcanics and granitoids are extensively feldspathized and silicified. The granitoids, and basic-intermediate volcanics, are albitized, while felsic volcanics are K-feldspathized. Metasomatism has severely modified K/Rb and Rb/Sr ratios, but not REE patterns, and is inferred to have occurred at relatively low T. Nametasomatism of the Upper Unit micaschists has produced albite porphyroblasts. Metasomatism postdates formation of the Upper Unit sediments, and is probably related to reaction with sea water that infiltrated the basement of volcanics and granitoids during deposition of these sediments. Rb-Sr whole-rock dating of extensively feldspathized intermediate-felsic metavolcanics gives an age of ca. 90 Ma, which suggests that the most extensive reaction coincided with expulsion of the trapped sea water during the early stages of the Alpine orogeny. The distribution of albitization vs. K-felds-pathization suggests that the type of metasomatism was controlled on a local scale by permeability and grain size, rather than by T variations.     

Magnetic properties of airborne particulate matter in Shanghai during dust storm events and the implications for heavy metal contaminant sources

Airborne particulate samples (including dust storm period samples) were collected from the Putuo, Qingpu and Minhang districts of Shanghai city from October, 2009 to October, 2010, and also tracked the dust transporting pathways from NW (Northwest) to SE (Southeast) including the cities of Xi’an, Beijing, Zhengzhou and Nantong, as a means of sampling the dust storm particulate matter in the spring of 2010. After measuring the magnetic parameters and the concentrations of particles and heavy metals, their magnetic properties were analyzed to track the source locations of heavy metal pollution during dust storm events, and then combined for backward trajectory analysis. It was found that the slightly polluted dust particles carried many contaminants during dust storm periods when the dust palls were transported by winter monsoon winds from the NW desert region towards the SE. The contaminants were further increased by contributions of fine SP&SD grains derived from local automobile exhausts in Shanghai as well as being enriched also in Northern cities during non-dust storm periods. A significantly positive linear relation was found between the χ_lf and SIRM of loess and the storm dust, indicating a similar material source for these two kinds of samples. A higher χ_lf and SIRM in storm dust content compared to loess suggests that storm dust contains not only materials from natural sources, but also those from partly anthropogenic sources. Backward trajectory analysis indicates intuitively the source region of the Shanghai storm dust. These conclusions have important scientific significance for research on long-distance transportation of contaminants (such as heavy metals) adsorbed onto airborne particulate matter during dust storm events.     

The ICL Network on “Landslides and Cultural & Natural Heritage (LACUNHEN)”

In recent decades, the concept of cultural heritage has evolved into one that encompasses an understanding of the history of humanity, together with scientific knowledge and intellectual attitudes. This changing concept has prompted a subsequent re-evaluation of what constitutes the outstanding universal values of World Heritage sites and the operational methods for implementing the UNESCO World Heritage Convention. The scope has broadened from studying a single monument in isolation to one that values a multidimensional, multiregional, and inter-disciplinary approach and encapsulates vast spans of human history. Within this broader view, landslides and more generally slope instabilities are an important factor endangering cultural heritage sites, especially prehistoric sites, earth/rock monuments, and archaeological sites affected by environmental processes and degradation. Natural and cultural heritage sites, as well as cultural landscapes, are then tied into a common framework that the Geological Society of America has defined “Men’s legacy to Earth and Earth’s legacy to Man”. On the other hand, not too much effort has been expended in the past to develop conservation policies systematically integrating geological, geomorphological, and engineering geological aspects into daily practices. The purpose of the “LAndslides and CUltural & Natural HEritage” thematic Network (LACUNHEN) is to create a platform for scientists and practitioners who are ready to jointly contribute to safeguarding relevant endangered Natural and Cultural Heritage sites (e.g., Machu Picchu). They will share and disseminate their respective experience, demonstrating how these special “objects” require approaches, techniques, and solutions that go far beyond traditional civil engineering perspectives.     

Radiation resistant of native Deinococcus spp. isolated from the Lout desert of Iran “the hottest place on Earth”

Two native ionizing radiation-resistant bacteria were isolated and identified from a soil sample collected from extreme conditions of the Lout desert in Iran. The hottest land surface temperature has been recorded in the Lout desert from 2004 to 2009. Also, it is categorized as a hyper arid place. Both ionizing radiation and desiccation may cause damage on genome. Soil sample was irradiated in order to eliminate sensitive bacteria then cultured in one-tenth-strength tryptic soy broth medium. Bacterial suspension used for radiation treatment. Morphological and physiological characterization and phylogenetic studies based on 16S rRNA gene sequence were used for identification. The cells were rod shape, non-motile, non-spore forming and gram positive. The 16S rRNA gene sequence showed 99.5 % of similarity to Deinococcus ficus. Phylogenetic dendrogram demonstrated that the isolates branched with D. xibeiensis, D. ficus and D. mumbaiensis. Both isolates were resistant to >15 kGy of gamma radiation and >600 J m² of UV radiation. This is the first report on radiation resistant bacteria belonging to genus Deinococcus isolated from the Lout desert of Iran.     

TL dating of loess in China

TL ages of 56 loess samples collected from Xinjiang and the middle reaches of the Yellow River were determined by using fine-grained quartz and man-made light source bleaching techniques.The results indicate that :1.The well-preserved loess sections in Xinjiang began depositing 400000 a ago.The loess/paleosol series may be comparable with that observed in the middle reaches of the Yellow River but the depositing time was probably delayed by 30000-50000a.2.The bottom boundary age of the Malan loess varies from one place to another.The TL dates can be divided into two group:70000-130000 a and 30000-50000 a.The TL data are con-sistent with the appearance of two warmer climate periods since the Pleistocene,indicating obvious regional differences in stratigraphic development of loess,i.e.,paleosol occurred in the warm climate period in the same location,but loess was deposited in other locations.The initial age of loess deposition tends to become older from west to east and from south to north .In contrast ,the cold cli-matic belt showed an opposite trend.The TL ages of loess provide strong evidence for the Quaternary stratigraphy throughout geological times and the shift tendency of climatic belt.3.The depositing rate of the Malan loess along the middle reaches of the Yellow River varies from place to place but the TL age shows a linear relationship with the depositing thickness.The de-positing rate of loess in the north is higher than that in the south,suggesting that loess materials are derived from desert areas of northern China.     

Plant migration and plant communities at the time of the “green Sahara”

Around 8500 cal years BP, at the time of the maximum of the African Humid Period, lakes and wetlands expanded in the present-day Sahara while large paleodrainages were formed or re-actived, in response to an orbitally-induced increase in monsoon rainfall. It has been suggested that the direct consequence of this increase in rainfall was the northward displacement of the Sahara/Sahel boundary, thought to have reached 23°N in central and eastern Africa. Here, we show a more complex situation characterized by an increase in biodiversity as the desert accommodated more humid-adapted species from tropical forests and wooded grasslands: tropical plant species now found some 400 to 500 km to the south probably entered the desert as gallery-forest formations along rivers and lakes where they benefited from permanent fresh water. At the same time, Saharan trees and shrubs persisted, giving rise to a vegetation that has no analogue today. In this article, we present distribution maps of selected plant species to show both the amplitude of the vegetation change compared to the present and the composition of the past plant communities. We also estimate the migration rate of tropical plant taxa to their northernmost position in the Sahara. This study is based on the use of several data sets: a data set of the modern plant distribution in northern Africa and a data set of modern and fossil pollen sites (from the African Pollen Database, http://fpd.mediasfrance.org/ and http://medias.obs-mip.fr/apd/).     

The transformation of amorphous silica to crystalline silica under hydrothermal conditions

Hydrothermal syntheses were made mainly in the binary system SiO₂-H₂O in a temperature range between 300 ° C and 500 ° C and pressures from 0.2 kbar up to 4.0 kbar with various starting materials. In this way the transformation behavior of different amorphous silicas via cristobalite and keatite to quartz were observed. This behavior depends mainly on the parameters: pressure, temperature, run duration and state of the starting material. Four reaction paths have been observed: in most experiments the complete reaction sequence “amorphous silica→cristobalite→keatite→quartz” took place. Less often the reactions: “amorphous silica→cristobalite→quartz” and: “amorphous silica→keatite→quarts” were observed. Very few samples were found with a direct transition of amorphous silica into quartz at high pressures. A kinetic model is given in form of a pressure-temperature-time diagram of the system SiO₂-H₂O under hydrothermal conditions.     

从陕西旬邑上新生界剖面看黄土高原新近系/第四系界线

新近系 /第四系界线在黄土高原大都以磁性 M/ Ga界线为界进行划分 ,它与岩性分界往往并不一致 ,后者都低或高于前者一小段距离。根据旬邑剖面的岩性、孢粉、古动物、磁化率、粒度及地化资料 ,并参考了其他一些剖面的岩性 ,认为以二者之间的过渡层底为界进行划分比较合理     

Chronology of late Pleistocene Pampa loess from the Córdoba area in Argentina

In Argentina, loess/palaeosol sequences were studied from the two sections at Monte Ralo and Corralito, located near to the city of Córdoba in the east of the Pampean ranges. Infrared optically stimulated luminescence (IRSL) and thermoluminescence (TL) dating techniques were applied to set up a more reliable chronological framework for the Upper Pleistocene loess record. IRSL ages increase with depth and are stratigraphically consistent. The oldest loess exposed correlates at least to the penultimate glaciation. The luminescence dating study gives evidence for humid climate conditions with soil formation during the last interglacial period and the middle pleniglacial correlating to Marine Isotope Stage (MIS) 5 and 3, respectively. Three extended periods of soil formation are recorded in the loess/palaeosol sequences at the Corralito section. These buried soils most likely correlate with the last interglacial and early last glacial period. During the Middle Pleniglacial, two palaeosols are intercalated in the loess successions. In the Córdoba area, the periods of increased loess accumulation and deposition of loessic sediments correlate with more arid and glacial periods during the Early Pleniglacial, the Middle Pleniglacial and the Late Glacial. Copyright © 2009 John Wiley & Sons, Ltd.     

Liquids in equilibrium with peridotitic mineral assemblages at high water pressures

Pressure-temperature conditions for which “andesitic” liquids (～60% SiO₂) may coexist with mineral assemblages of the type magnesian olivine + orthopyroxene + clinopyroxene±amphibole±phlogopite have been investigated, both by means of partial melting experiments on the pyrolite model composition, and by experiments involving addition of olivine to andesite or basaltic andesite compositions at or near their liquidus temperatures. In the latter experiments, reaction relationships between quartz-normative liquid and olivine were made to proceed until olivine persisted. The composition of the final liquid in equilibrium with olivine (plus pyroxenes etc.) was then estimated by microprobe analysis of its quench products (glass, quench crystals). The inferred liquid compositions were tested for equilibrium with coexisting crystals using criteria based on mass balance within the total assemblage, equilibrium element partition relationships, and the requirement that the liquidus temperatures and near-liquidus crystalline phases of these compositions should closely match the temperature of the original olivine-addition experiment and the crystalline phases developed during it. At 1000° C–1050° C, liquids which satisfy these criteria for equilibrium with assemblages which include olivine are “andesitic” (58–60% SiO₂, 5–12% normative Qz) only at water pressures ≤ 10kb. At 15 kb, liquids in equilibrium with olivine at 1000° C and 980° C have ～56% SiO₂, high alkali contents, and 5–10% normative olivine. Similar compositions are in equilibrium with orthopyroxene and garnet alone at 20 kb. These results show that andesitic magmas are unlikely to be produced by melting of a peridotitic mantle at pressures >10 kb (depths>35 km). If hydrous, but otherwise geochemically primitive peridotitic compositions are partially melted at pressures<10 kb, then “andesitic” products will be much more magnesian and poorer in alkalies than typical natural andesites. These conclusions raise serious difficulties for models of andesite genesis by the melting of hydrous peridotitic mantle immediately overlying Benioff zones.     

Comment: A study of “probabilistic” and “deterministic” geostatistics

Stochastic process theory involves integrals of measurable functions over probability measure spaces. One of these is the ensemble space, Ω, whose members are sample functions on Euclidean spaceR ^k and the other isR ^k itself. What geostatisticians call the “theory of regionalized variables” is said to based on stochastic theory. A recent paper inMathematical Geology proclaims a distinction between “probabilistic” and “deterministic” geostatistics. The former is said to rely on “ensemble integrals” over Ω and the latter on “spatial integrals” overR ^k. This study shows that the proposed distinction rests on an arbitrary choice between two estimators for the covariance of a stochastic process; neither is an ensemble integral, both are spatial integrals, and both are Kolmogorov inconsistent. The “deterministic” estimator is identical with that of classical bivariate least-squares regression in which “spatial structure” is of no consequence. This study shows that both stochastic models are suboptimal approximations to the unique nonstationary classical statistical multivariate regression model generated by each sample pattern. The stochastic process model and its “spatial continuity measures,” thus, appear as questionable mathematical embellishments on suboptimal estimates, correspondence with geomorphic reality is tenuous, and estimates are biased and distorted. Various related misconceptions in the paper are also discussed.     

萨拉乌苏河地区地层中的碎屑矿物及其所反映的中更新世末期以来之气候环境变化

文章根据对萨拉乌苏河地区第四纪地层中的碎屑矿物分析结果,将重矿物按其抗化学风化的能力不同分为不稳定、较稳定、稳定和极稳定四种类型,不同层位的重矿物类型的百分含量不同,从而可求出重矿物的风化系数HW。不同时期地层的HW不同,而HW的大小变化与化学风化的程度有很大关系,一般来说,化学风化作用强,HW相应变小。而化学风化作用的强弱又主要受气候的影响,从而可推测该时期气候环境的变化。     

Measurements of volcanic SO2 and CO2 fluxes by combined DOAS,Multi-GAS and FTIR observations: a case study from Turrialba and Telica volcanoes

Over the past few decades, substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic SO₂ emissions. However, measurements of CO₂ emissions still present many difficulties, partly due to the lack of instruments that can directly measure CO₂ emissions and partly due to its strong atmospheric background. In order to overcome these difficulties, a commonly taken approach is to combine differential optical absorption spectroscopy (DOAS) by using NOVAC scan-DOAS instruments for continuous measurements of crateric SO₂ emissions, and electrochemical/NDIR multi-component gas analyser system (multi-GAS) instruments for measuring CO₂/SO₂ ratios of excerpts of the volcanic plume. This study aims to quantify the representativeness of excerpts of CO₂/SO₂ ratios measured by Multi-GAS as a fraction of the whole plume composition, by comparison with simultaneously measured CO₂/SO₂ ratios using cross-crater Fourier transform infrared spectroscopy (FTIR). Two study cases are presented: Telica volcano (Nicaragua), with a homogenous plume, quiescent degassing from a deep source and ambient temperature, and Turrialba volcano (Costa Rica), which has a non-homogeneous plume from three main sources with different compositions and temperatures. Our comparison shows that in our “easier case” (Telica), FTIR and Multi-GAS CO₂/SO₂ ratios agree within a factor about 3 %. In our “complicated case” (Turrialba), Multi-GAS and FTIR yield CO₂/SO₂ ratios differing by approximately 13–25 % at most. These results suggest that a fair estimation of volcanic CO₂ emissions can be provided by the combination of DOAS and Multi-GAS instruments for volcanoes with similar degassing conditions as Telica or Turrialba. Based on the results of this comparison, we report that by the time our measurements were made, Telica and Turrialba were emitting approximately 100 and 1,000 t day^?1 of CO₂, respectively.     

Late Pleistocene Climatic Variations at Achenheim, France, Based on a Magnetic Susceptibility and TL Chronology of Loess

New field investigations of the Achenheim sequence (Alsace, France) allow for the characterization of variations in the low-field magnetic susceptibility over most of the last climatic cycle, i.e., the past 130,000 yr. New stratigraphic data and thermoluminescence measurements permit reassessment of the previous chronological interpretation of the Upper Pleistocene at Achenheim. A high-resolution analysis of magnetic susceptibility discloses the occurrence of a fine-grained “marker” horizon which was also found recently in another section. This horizon is interpreted as a small-scale dust layer deposited prior to the main interval of loess deposition. The horizon, deposited at the marine isotope stage (MIS) 5/4 boundary, has been found in other loess sequences and is especially prevalent in central Europe. It is characterized by low susceptibility values and a grayish color. New thermoluminescence dates indicate that the loess deposition took place after the MIS 5/4 boundary, i.e., after 70,000 yr. These results are consistent with the Greenland GRIP ice-core dust record which also demonstrates a dusty atmosphere after 72,000 yr ago. On a more regional scale, the Achenheim loess sequence demonstrates a reliable correlation between the western side of the Eurasian loess belt and the dust record of the Greenland ice cores.