Granulometric Spectrum Research Articles

СТРОЕНИЕ ДОЛИНЫ РЕКИ ШУРА-ОЗЕНЬ НА УЧАСТКЕ ЭОЛОВО-АККУМУЛЯТИВНОГО КОМПЛЕКСА “САРЫКУМ” (РЕСПУБЛИКА ДАГЕСТАН), "Геоморфология"

В работе, на основе гранулометрического, минералогического анализов и геолого-геофизического профилирования, излагаются результаты изучения строения долины р. Шура-Озень (Республика Дагестан, Россия), берущей начало в низкогорье северо-востока Большого Кавказа и впадающей в Каспийское море в северной части г. Махачкала. В долине реки, на ее участке близ эолово-аккумулятивного комплекса “Сарыкум”, который является одним из крупнейших в Евразии изолированных песчаных массивов, выделены две группы террас, резко различающиеся своим строением. Первая группа - это пойменный комплекс и высокие (V и VI) террасы с закономерным чередованием по профилю пойменных и русловых фаций аллювия нормальной мощности. Вторую группу образуют I, III и IV террасы, в профиле которых очевидна резко увеличенная мощность пойменных фаций аллювия (особенно у IV террасы), представленных, главным образом, разными по гранулометрическому составу песками. Время формирования VI террасы долины реки нами предполагается как доательское (позднегирканское ( ), ранее 44-41 тыс. кал.л.н.), V террасы - как раннехвалынское (ок. 40-33 тыс. кал.л.н.), IV террасы - среднехвалынское (ок. 33-(25)20 тыс. кал.л.н.), между двумя глубокими врезами реки, приуроченными к эльтонской и енотаевской регрессиям палео-Каспия. Время формирования террасы III - поздняя хвалынь (ок. (25)20-12 тыс. кал.л.н.), до мангышлакской регрессии. Возраст низких террас и поймы долины - голоцен. Следовательно, время заложения долины р. Шура-Озень в ее современном виде на данном участке течения, как и время формирования песков Сарыкума как изначально преимущественно пролювиально-дельтовых образований, - свыше 44-41 тыс. кал.л.н. (или 41-37 тыс. л.н.). Анализ гранулометрических спектров аллювиальных отложений позволил сделать важный вывод о том, что наиболее активная фаза формирования дюн эолово-аккумулятивного комп­лекса “Сарыкум” проходила в эпоху, предшествовавшую образованию речных террас, т.е. после формирования пролювиально-дельтовых песков, но до заложения долины р. Шура-Озень. Предполагается генетическая связь реликтовых стадийных прибрежно-морских песчаных кос и галечного берегового вала, расположенных севернее Сарыкума, соответственно с аллювием III и V террас долины реки.

CRYOGENIC PROCESSES IN LOESS

This paper presents a new approach to the analysis of the genetic nature of the mineral substance of loessial rocks. At the present time, the prevailing view on this issue is the eolian accumulation of loess, while the influence of other factors of formation has not been practically taken into account. However, loess accumulation can be explained by other mechanisms, e.g., active processes of cryogenic weathering under a very harsh climate. The latter concept is based on the results of analysis of wedge-shaped structures in loess thickness, as well as numerous data of spore-pollen, microfaunistic, and other types of analysis. Further developing concepts of loess formation, the authors made an attempt to assess the degree of influence of cryogenic processes on the composition and structure of loess. The proposed method is based on a differentiated analysis of the distribution of the main rock-forming minerals (quartz and feldspars) along the granulometric spectrum. Two criteria are proposed − the coefficient of cryogenic contrast and the heavy fraction coefficient (i.e., the coefficient of distribution of heavy minerals) − which allow determining the degree of participation of cryogenic processes, as well as aeolian and aqueous sedimentation, in the formation of loessial rocks. This method was used to study two sections of loessial thickness − in the south of the Russian Plain and within the Loess Plateau of China. The results of the study revealed the role of cryogenic factors in the formation of the composition of the loess horizons of soil-loess sequences of different territories. Particularly clearly the effect of cryogenesis was manifested in the loess section in the south of the Russian Plain. In the section of the Loess Plateau, only the youngest deposits of the last formation stage are affected by cryogenesis. It follows that not only within the long-term periglacial permafrost zone, but also under the conditions of seasonal freezing in the Pleistocene, the processes of cryogenic transformation of deposits could have developed, which contributed to the formation of the composition and properties of loess of sufficiently high thickness.

AEOLIAN-ACCUMULATIVE COMPLEX SARYKUM AS A UNIQUE GEOMORPHIC OBJECT OF RUSSIA: STRUCTURE, GENESIS AND SANDS SOURCES

Aeolian-accumulative complex Sarykum is one of the highest isolated (i.e. formed away from the deserts) sandy landforms in Eurasia, located within the Terek-Sulak lowland plain at the north-eastern foothill of the Caucasus Mountains, 16–17 km towards WNW of the Makhachkala City port of Caspian Sea (Republic of Dagestan, Russia). On the basis of particle size distribution and mineralogical analysis of 59 sandy samples, the heterogeneous structure of the complex is defined. The coarsest sandy material (modal values are 352 micron and more) composes the central dune-ridge segment of Sarykum (of so-called Great (or West) Sarykum). The further from the dune constructions to the periphery, the thinner the average dimension of the sand particles and smaller the modal values (249 micron and less) of their granulometric spectra. This grain size distribution can be explained not only by windy sorting of the sands and further aeolian recast of dune-ridge segment, but also by spatial features of the facial changes during the period of initial sandy accumulation, and also by the differences in composition of rocks, which were the sources of denudation. In the vertical structure of Sarykum the heterogeneity is also expressed. It is associated with temporary changes of sandy sedimentation conditions in the region. So, the dune-ridge segment of Great Sarykum can be represented as a system of consistently accumulated sandy layers (lenses?) (which includes the gravelly sands), which differ in composition and age, having apparently the coarsest content in the middle part of its vertical geological cross-section. The material of overwhelming majority of the selected samples belongs to mineral group of quartz sands (quartz content is over 90%) and subgroup of quartz subarkose (quartz content is 80–90%). Moreover, the aeolian (defl ated) sands of the dune-ridge segment and its underlying cross-bedded sands of Great Sarykum entirely belong to the first group; the hilly and peripheral sands, which characterized by fine granulometry, refer to the second mineral subgroup. The Sarykum’s structure is due to the combination of gravelly sands, formed by the river Shura-Ozen’ deltaic accumulation in the Late Quaternary, and sandy (with gravels and pebbees) deposits proluvially and deluvially dislocated to the recent Sarykum massif territory from the slopes of the nearby Narat-Tube mountain range. The mixing of originally and compositionally different sediments that formed the Sarykum complex, likely have the complicated history, following by the staged changes of the periglacial landscape-climatic conditions in the Late Quaternary.

THE ROLE OF CRYOGENIC PROCESSES IN THE FORMATION OF LOESS DEPOSITS

The paper describes a new approach to the analysis of the genetic nature of mineral substances in loess deposits. In permafrost under the influence of multiple alternate freezing and thawing in dispersed deposits, quartz particles accumulate the 0.05-0.01 mm fraction, while feldspars are crushed to a coarse fraction of 0.1-0.05 mm. In dispersed sediments formed in temperate and warm climatic zones, the granulometric spectrum of quartz and feldspar has the opposite pattern. The proposed methodology is based on a differential analysis of the distribution of these minerals by the granulometric spectrum. We have proposed two criteria - the coefficient of cryogenic contrast (CCC) and the coefficient of distribution of heavy minerals, which allow determination of the degree of participation of cryogenic processes in the formation of loess sediments and processes of aeolian or water sedimentation.

Testing for nematode–granulometry relationships

The majority of studies have advocated that diver- sity of marine nematodes increases with increasing sediment grain size, although the opposite trend has also been sug- gested. The controversy is partially caused by not taking into account the effect of density on patterns of diversity and by analyzing datasets from different environments. The present study investigated nematode assemblages from sediments varying from very fine sand (mean grain size of 0.12 mm) to very coarse sand (1 mm) in shallow sublittoral marine envi- ronments. Contrary to previous studies, species richness was constant along the granulometric spectrum, despite significant changes in composition. The dominant genera were separated into five groups according to their optimum distribution and there was little overlap between these groups. Concepts from the niche theory explain to some extent the observed patterns. For instance, some of the coexisting genera were from differ- ent feeding types.

Characterization of a paint drying process through granulometric analysis of speckle dynamic patterns

Dynamic speckle patterns are generated by laser light scattering on surfaces that exhibit some kind of activity, due to physical or biological processes. The characterization of this process is carried out by studying the texture changes of auxiliary images: temporal history of the speckle pattern (THSP). The drying process of water borne paint is studied through a method based on mathematical morphology applied to the THSP image processing. It is based on obtaining the granulometry of these images and their characteristic granulometric spectrum. From the granulometric size distribution of each THSP image four parameters are obtained: mean length, standard deviation, asymmetry and kurtosis. These parameters are found to be suitable as texture features. The Mahalanobis distance is calculated between the texture features of the THSP images representative of the temporary stages of the drying process and the features of the final stage or pattern texture. The behavior of the distance function describes satisfactorily the drying process of the water borne paint. The results are compared with other methods. Compared with others, the granulometric method reported in this paper distinguished by its simplicity and easy implementation and can be used to characterize the evolution of any process recorded through dynamic speckles.

Airborne silica levels in an urban area

In order to evaluate the exposure levels of the general population we studied the concentrations of silica particles in the inhalable particulate fraction (PM10) in different meteorological-climate periods in an urban area of Rome. In order to determine the concentration and the granulometric spectrum of silica particles, PM10 sampled by a cascade impactor was analysed by X-ray diffractometry (XRD) and by scanning electron microscopy equipped with a thin-window system for X-ray microanalysis (SEM/EDX). Over the period September 2004-October 2005 the abundance of silica particles as evaluated by SEM/EDX ranged from 1.6 to 10.4% of the total PM10 particulate, with a weight concentration of free crystalline silica, evaluated by XRD, in the range 0.25-2.87 microg/m3. The mean diameter of silica particles ranged from 0.3 to 10.5 microm, with more than 87% of particles having a diameter of less than 2.5 microm. The correlations between SEM/EDX and XRD data seem to suggest that the airborne silica particles in the urban location studied were mainly in the form crystalline silica. A strong relationship was found between the meteorological-climate conditions and the concentration level of free crystalline silica. This result suggests that the Southern winds from the Sahara desert carry an important amount of silica particles into Mediterranean Europe.

Emission comparison of urban bus engine fueled with diesel oil and ‘biodiesel’ blend

The chemical and toxicological characteristics of emissions from an urban bus engine fueled with diesel and biodiesel blend were studied. Exhaust gases were produced by a turbocharged EURO 2 heavy-duty diesel engine, operating in steady-state conditions on the European test 13 mode cycle (ECE R49). Regulated and unregulated pollutants, such as carcinogenic polycyclic aromatic hydrocarbons (PAHs) and nitrated derivatives (nitro-PAHs), carbonyl compounds and light aromatic hydrocarbons were quantified. Mutagenicity of the emissions was evaluated by the Salmonella typhimurium/mammalian microsome assay. The effect of the fuels under study on the size distribution of particulate matter (PM) was also evaluated. The use of biodiesel blend seems to result in small reductions of emissions of most of the aromatic and polyaromatic compounds; these differences, however, have no statistical significance at 95% confidence level. Formaldehyde, on the other hand, has a statistically significant increase of 18% with biodiesel blend. In vitro toxicological assays show an overall similar mutagenic potency and genotoxic profile for diesel and biodiesel blend emissions. The electron microscopy analysis indicates that PM for both fuels has the same chemical composition, morphology, shape and granulometric spectrum, with most of the particles in the range 0.06–0.3 μm.

Submicron desert dusts: A sandblasting process

Mass size distributions of the major elements of the mineral aerosol of northern Sahara were obtained from measurements carried out with an inertial cascade impactor. A fitting procedure by data inversion was applied to these data. This technique considers the major mechanisms of nonideal behavior such as particle bounce‐off, wall losses and cross sensitivity which affect the accuracy of impactor measurements of aerosol size distribution. Accurate size distributions of Saharan aerosol (range 0.1–20 μm) were so obtained for different conditions of soil mobilization. These measurements, coupled with wind speed information, show the shape of the size distribution for desert aerosols in the considered range to be characterized by a similar pattern with a common mode of particles having diameter between 1 and 20 μm whatever the weather conditions. A second mass peak of submicron particles appears when the wind speed increases above the threshold value for erosion. Scanning electron microscope photographs indicate that the whole granulometric spectrum of the sampled aerosol between 0.1 and 20 μm mainly consists of clay easily disaggregated by sandblasting. The common origin of submicron particles with those between 1 and 20 μm is established by showing the similar composition of dusts in the both modes. The results suggest that the presence of submicron mineral particles during dusty and sandstorm conditions is consistent with a sandblasting process.

A numerical simulation of the Plinian Fall Phase of 79 A.D. eruption of Vesuvius

The tephra transport and fallout during the Plinian phase of the 79 A.D. eruption of Vesuvius has been numerically simulated by using an advection‐diffusion model based on a continuity equation for the mass concentration in which wind field, atmospheric diffusion, and gravity settling are considered. The solution of the equation has been obtained on a nonuniform three‐dimensional grid to optimize the computation time and to reduce the errors. The input data are (1) the total erupted mass, (2) the variation with time of the column height, (3) the particle population in terms of the settling velocity, and (4) the wind field. The vertical mass distribution of the particles which leave the column is given by an empirical formula (Suzuki, 1983), whose parameters are obtained from data of Carey and Sigurdsson (1987) and best fitting with field data. Two distinct phases have been distinguished in the eruption: (1) related to white phonolitic pumice fallout and (2) dominated by the emission of gray tephritic‐phonolite pumice. According to the literature the total duration of the pumice fallout was about 19 hours with column height ranging between about 14 and 32 km. The “white phase” has been estimated to have had 9 hours duration, while the “gray phase” lasted 10 hours. Magma discharge rate has been calculated assuming a fourth power relationship with column height. Total erupted volumes of 1.0 and 2.6 km3 of dense rock equivalent products have been assumed for the white and the gray phases, respectively (Sigurdsson et al., 1985). The particle population of the cloud has been assumed to correspond to that of a pyroclastic flow deposit related to a nearly total column collapse. The wind field results from a 60° clockwise rotation of the presently most frequent wind distribution field during the summer reduced in speed module of about 40%. The simulated ground thicknesses generally agree with the actual ones. The computed granulometric spectra at specific localities are in excellent agreement with the measured ones. As a whole, the simulation was successful. This fact emphasizes the significant consequences that the used model with a suitable choice of the input parameters can have for the establishment of a truly probabilistic air fall hazard map of Vesuvius.

Granulometric spectrum of aerosol particles in slightly-polluted seaside atmosphere

We carry out a granulometric study of atmospheric aerosol by recovering the particles on the eight stages of an Andersen impactor, and on a Nuclepore filter placed behind. The analyses are done by electron and optical microscopy. We obtain in this way a granulometric spectrum ranging (in diameters) from 8.5 10 −3 μm to 70 μm. A statistical study permits us to prove the existence of three modes for the particles of diameters less than the micron. For the large particles, we measure the coefficient B of Junge's Law. Finally, it is possible for us to determine the principal characteristics of the Andersen (E.C.S.; N.M.D.; M.M.D.).