North Caspian Region Research Articles

A New Mineral Calcioveatchite, SrCaB11O16(OH)5·H2O, and the Veatchite–Calcioveatchite Isomorphous Series

The new mineral calcioveatchite, ideally SrCaB11O16(OH)5·H2O, is a Ca-Sr-ordered analogue of veatchite. It was found at the Nepskoe potassium salt deposit, Irkutsk Oblast, Siberia, Russia in halite-sylvite and sylvite-carnallite rocks, with boracite, hilgardite, kurgantaite, hydroboracite, volkovskite, veatchite, anhydrite, magnesite, and quartz. Calcioveatchite forms prismatic or tabular crystals up to 1 × 1.5 × 3 mm3 and crystal clusters up to 3 mm across. It is transparent and colourless with vitreous lustre. Calcioveatchite is brittle, cleavage is perfect on {010}, the Mohs’ hardness is ca 2, Dmeas is 2.58(1), and Dcalc is 2.567 g cm−3. Calcioveatchite is optically biaxial (+), α = 1.543(2), β = 1.550(5), γ = 1.626(2), 2Vmeas = 30(10)°, and 2Vcalc = 35°. The average chemical composition (wt.%, electron microprobe, H2O calculated by stoichiometry) is: CaO 7.05, SrO 20.70, B2O3 61.96, H2O 10.22, and total 99.93. The empirical formula, calculated based on 22 O apfu = O16(OH)5(H2O) pfu, is Sr1.23Ca0.78B10.99O16(OH)5·H2O. Calcioveatchite is monoclinic, space group P21, a = 6.7030(3), b = 20.6438(9), c = 6.6056(3) Å, β = 119.153(7)°, V = 798.26(8) Å3, and Z = 2. Polytype: 1M. The strongest reflections of the powder XRD pattern [d,Å(I,%)(hkl)] are: 10.35(100)(020), 5.633(12)(110), 5.092(10)(120), 3.447(14)(060), 3.362(13)(101, 051), 3.309(38)(–102), 2.862(10)(012), and 2.585(19)(080). The crystal structure was solved based on single-crystal XRD data, R1 = 0.0420. Calcioveatchite (calcioveatchite-1M) is an isostructural analogue of veatchite-1M with the 11-fold cation polyhedron occupied mainly by Sr [Sr0.902(8)Ca0.098(8)] whereas the 10-fold polyhedron is Ca dominant [Ca0.686(7)Sr0.314(7)]. The chemical composition of veatchite from five localities in Russia (Nepskoe), Kazakhstan (Shoktybay and Chelkar in the North Caspian Region), and the USA (Tick Canyon and Billie Mine in California) was studied, and it is shown to exist in nature as a continuous, almost complete isomorphous series which extends from Ca-free veatchite, Sr2B11O16(OH)5·H2O, to calcioveatchite with the composition Sr1.14Ca0.87B10.99O16(OH)5·H2O.

Airborne and Underwater Noise Produced by a Hovercraft in the North Caspian Region: Pressure and Particle Motion Measurements

The measurements of airborne and underwater noise radiated by a Griffon BHT130 hovercraft were conducted in the Ural-Caspian Channel and in the North Caspian Sea. This type of hovercraft is being used for all-season cargo and crew transportation to oil and gas platforms within the environmentally sensitive area of the Ural River estuary known for its abundant bird and fish fauna. Several field campaigns were organized from 2017 to 2022 to measure and analyze acoustic noise levels simultaneously in the air and underwater at various sites and hovercraft speeds. Airborne noise levels were estimated according to ISO 2922:2020, 2021. Underwater noise study included not only acoustic pressure recordings but also particle velocity measurements with a self-designed pressure gradient sensor (PGS), which is important since the hearing of the majority of fish perceives the sound in terms of particle motion. This study is the first to report the particle velocity levels formed underwater during hovercraft passages. The minimum levels of underwater noise, 100 dB re 1 µPa (pressure), 45 dB re 1 nm/s (particle velocity), and airborne noise, 93 dBA re 20 µPa (pressure), normalized to a distance of 25 m were observed for the hovercraft passages at a cruising speed of 7–15 m/s. Thus, this speed interval can be recommended as an optimum to minimize an acoustic impact on ornitho- and fish fauna. The directivity of the hovercraft noise was estimated for the first time and utilized for noise mapping of the Ural-Caspian Channel. The possible hydrodynamic effect of a passing hovercraft is discussed.

Impact of gas composition and reservoir heterogeneity on miscible sour gas flooding — A simulation study

Proper handling of the produced sour gas is a big challenge for operating companies due to the serious environmental and technical problems caused by H2S and CO2. The reinjection of the produced sour gas into oil reservoirs is an environmentally friendly as well as an economically attractive method due to the low investment cost and incremental oil recovery. However, the sour gas injection for enhanced oil recovery (EOR) is a relatively new approach with numerous uncovered perspectives, especially in a heterogeneous reservoir. The objective of this study is to investigate the effect of gas composition and reservoir heterogeneity on the miscible displacement of reservoir oil using sour gas.The reservoir oil consisting of 15 mol% H2S and 4 mol% CO2 from an oilfield in the North Caspian region was used. First, the phase behavior alteration of reservoir oil due to the injection of various gases, namely H2S, CO2, CH4, acid, and sour gas was analyzed. Then, the effect of gas type on minimum miscibility pressure (MMP) was investigated based on a semi-analytical tie-line method. Moreover, 2D and 3D numerical simulations were conducted to understand the oil recovery performance of various gas injection options and the effect of permeability heterogeneity on sour gas flooding efficiency. The findings showed that higher H2S content in the injected gas narrows the two-phase envelope and decreases the bubble point pressure. Moreover, it was observed that MMP decreases with increasing H2S concentration, which provides a favorable condition for achieving miscibility. Additionally, an increase in H2S concentration in sour gas improves its oil recovery efficiency by extending gas breakthrough time and elongating the plateau period of oil rate. These results are useful for designing, optimizing, and implementing sour gas injection for EOR in oil reservoirs that have access to sour gas sources.

ВЛИЯНИЕ НЕКОРНЕВЫХ ПОДКОРМОК НА АДАПТАЦИОННЫЕ ХАРАКТЕРИСТИКИ СОРТОВ СЛИВЫ В АРИДНЫХ УСЛОВИЯХ АСТРАХАНСКОЙ ОБЛАСТИ

The article discusses the effect of the foliar application of fertilisers on the leaf surface parameters of garden plum varieties grown in the arid light chestnut soils of the North Caspian Region. The research aimed to study the effect of foliar application of macro- and microfertilisers on the leaf surface parameters (leaf area, leaf area of one tree, leaf area per 1 ha) in plum varieties grown in the extremely arid conditions of Astrakhan region. The study was carried out in the experimental field of Caspian Agrarian Federal Scientific Center of the Russian Academy of Sciences. The field was laid out in 2014. Observations and records were performed in 2019–2021. The research used plum varieties such as Kabardinskaya Rannyaya, Ispolinskaya, Stanley and foliar fertilisers such as Master, Aquarin, Ultramag boron and Ultramag calcium. The chief production indices include leaf area, photosynthetic potential and photosynthesis net productivity. The indices have a close relationship with yield indices. The optimal leaf area is an important index of the technology and is crucial for the efficient absorption of light energy to initiate photosynthesis [1]. The effect of simultaneous application of microfertilisers Aquarin and Ultramag boron and Ultramag calcium on the plum leaf surface parameters was analysed. The research showed that varieties Kabardinskaya Rannyaya and Stanley responded most favourably to the fertiliser application. Variety Ispolinskayaya showed a high response to fertiliser Master. The experimental variant that simultaneously applied fertilisers Aquarin, Ultramag boron Ultramag calcium demonstrated the largest leaf area per 1 ha compared to the control (3433 m2 ). In terms of varieties, variety Ispolinskaya had the largest leaf area per 1 ha compared to the control (3020 m2 ).

Geodynamic and geological factors in the formation of large hydrocarbon deposits in subsalt sediments of the North Caspian region

Background. The Astrakhan-Primorsk region of oil and gas deposits located in the North Caspian region is one of the world’s largest reserves of hydrocarbons. This region stretches from land in the northwestern part of the Caspian basin, through the northern waters of the Caspian, to the south-eastern land part of the region under consideration.Aim. To identify geodynamic and geological factors in the formation of large hydrocarbon deposits in subsalt sediments in the complex structure of the North Caspian region of the Caspian syneclise. Materials and methods. An analysis of data on the geodynamic and geological evolution of the North Caspian region of the Caspian syneclise revealed specific features of its geological structure and development.Results. The nature of the formation series, as well as the geodynamic and geological conditions (the presens of spreading and subduction zones that caused an intense heat flow, the presense of an isolated sedimentation basin with intensive accumulation of carbonates in the Upper Devonian-lower Permian, a powerful salt-bearing Kungurian cap) were favourable for the generation, migration and accumulation of hydrocarbons in large tectonic-sedimentary Upper Devonian–Lower Permian uplifts characteristic of the Astrakhan-Primorsk oil-and-gas bearing region of the North Caspian. These uplifts were formed by shelf bioherms, barrier reefs and large reeftogenic atolls and emerged through ancient troughs. The large hydrocarbon accumulations, such as Kashagan, Tengiz, Astrakhanskoye and Korolevskoye, with high specific hydrocarbon reserves (more than 100 thousand/km2) are associated with these troughs.Conclusion. During the Upper Paleozoic, the main paleodepressions of the isolated basin of the North Caspian underwent a steady and long-term subsidence process, favourable for the accumulation of a thick stratum of carbonate (mainly reef) formations. This period was also characterized by the geothermal and baric conditions necessary for the transformation and subsequent migration of hydrocarbons from oil- and gas-producing complexes to reservoirs, which were mainly presented by massive carbonate formations of reef genesis. The as-formed deposits were preserved by thick salt-bearing Kungurian sediments. Directions for prospecting and exploration works aimed at discovering new hydrocarbon deposits in the subsalt sediments of the region were outlined.

Activation of Formation of Hydrocarbon Fluidizites under the Conditions of Shear Geodynamic Regime of the Caspian Region (Russian–Kazakh Sector, Russia)

The paper presents the results of the study of objects spatially related to extremely high hydrocarbon (HC) emissions identified in the North Caspian Sea. The analysis of variable geological–geophysical parameters in these objects showed (i) a high correlation with large destruction zones of the crust, (ii) the occurrence in negative forms of the top of the consolidated crust, (iii) elevated Moho top in areas of their occurrence, and (iv) their coincidence with near-shear depressions in the sedimentary sequence. These objects are revealed on the basis of surface reflection. The study of their spatial location allowed them to be correlated with the main clusters of petroleum formation, which can be identified from geological prospecting data. In the South Caspian Sea, petroleum clusters are studied by both seismic survey and drilling up to 7 km. The results of these comprehensive studies substantiate the conclusion on the formation of excitation sources under certain conditions at a deep horizon of the crust favorable for HC generation. The summarized materials from the North and South Caspian Sea suggest that significant areas of higher HC emissions are caused by large-volume fluidizites that formed in the petroleum clusters. These objects occur in the southern areas of the North Caspian region under dominant shear geodynamic regime. The position of the negative structures of the platform cover near the zones of transregional strike-slip faults causes their near-shear type. The association of HC fluidizites with near-shear depressions is caused by their location in the extension areas of the crust favorable for the formation of pull-apart structures. The correlation of fluidizites with various structural-tectonic and sedimentation factors indicates the key role of the deep geodynamic regime in the formation of similar objects.

Интродукция сорго многолетнего в почвенно-климатические условия Северного Прикаспия

В настоящее время обеспеченность полноценными кормами животных, пасущихся на природных пастбищах Прикаспия, очень низка она составляет в среднем по регионам от 10 до 41. Правильный подбор видов и сортов кормовых растений, продуктивных и устойчивых, это первый этап создания прочной кормовой базы. Одним из путей решения этой проблемы является интродукция, то есть натурализация и акклиматизация растений в новых для них условиях среды. Интродукция растений особенно актуальна для регионов со сложными природноклиматическими условиями. Приведены результаты исследования возможности интродукции кормового растения сорго многолетнее (Sorghum derzhavinii Tzvel.) в полупустынных почвенноклиматических условиях Северного Прикаспия. Регион проведения опыта Астраханская область. Коэффициент аридности составляет 0,11 0,30 (сильно аридная зона). За год осадков выпадает в пределах 125 265мм. Продолжительность периода с температурами выше 10С составляет 165 170 дней. Сумма эффективных температур достигает 3200 3500С. Испаряемость в 3 5 раз превышает количество выпавших осадков. Вероятность сухих и засушливых лет превышает 60. По результатам исследования было выявлено, что сорго многолетнее является неприхотливым к почвенным условиям растением, способным к произрастанию на малогумусных (0,75) солонцеватых почвах. Лучшие показатели урожайности зелёной массы отмечены у сорта Травинка в варианте 40 тыс. растений на 1 га: при поливе 41,6 т/га, на богаре 7,9 т/га у сорта Караван при густоте стояния 20 тыс. растений на 1 га: при поливе 24,8 т/га, на богаре 3,9 т/га. С 1 га кормового угодья сорго можно получить при поливе 2,2 8,5, на богаре 0,4 2,5 т корм. ед. Pastures of the Caspian region provide insufficient amount of highquality fodder, satisfying only 10 41 of total demand. Stabilization of forage resources requires optimal combination of highproductive and resistant crop species and varieties. Introduction of new crops into local environment is one of the ways improving forage availability, particularly for the regions with severe climate. Performance of perennial sorghum (Sorghum derzhavinii Tzvel.) was tested under strong dry climate in the Astrakhan region. Annual precipitation rate is 125 265 mm. Temperature of above 10С stays for 165 170 days. Growing degree days reach 3200 3500С. Evaporation rate exceeds precipitation by 3 5 times. Probability of dry years reaches 60. Sorghum showed good adaptability to soil and was able to grow on lowhumus (0.75) alkaline soil. Variety Travinka performed the best under plant density of 40 thousand plants per 1 ha: when irrigating 41.6 t ha1, under dry farming 7.9 t ha1. Karavan yielded the most under plant density of 20 thousand plants per 1 ha: under water supply 24.8 t ha1, without irrigation 3.9 t ha1. Sorghum could yield 2.2 8.5 and 0.4 2.5 t feed units ha1 under irrigation and dry conditions, respectively.

Using Earth Remote Sensing to Study the Parameters of the Morphological Structure of the Ridge Landscape in the North Caspian Region

This paper reports investigation data on ridge landscape patterns (formed by Baer knolls) in the North Caspian region obtained by mathematical approaches to landscape morphology. The investigation procedure involves remote sensing data and mathematical methods. A mathematical analysis of six sample areas has revealed that perimeters and diameters of the ridges fit the lognormal distribution. Discrete indicators that characterize the ridge location are compliant with the Poisson’s distribution in most cases. Due to river erosion activity, which destroys the knolls, their diameters do not fit the lognormal distribution anymore. The arguments have been considered in favor of various theories of the Baer knolls origin from the standpoint of quantitative features of the morphological structure.

Circulation of Yersinia pestis in the Volga-Ural Sandy Focus: Spatiotemporal Analysis

Aim . The present paper provides a comparative analysis of the phylogenetic relationship between Yersinia pestis strains isolated in the Volga-Ural sandy natural focus during the periods of 1912-1945 and 1963-2003, which were characterised by different levels of epidemic activity, in order to identify the spatiotemporal patterns in the circulation of the plague pathogen in the North Caspian region. Materials and methods . We studied the properties and performed whole-genome sequencing of 18 Y. pestis strains from the Volga-Ural sandy focus, along with 12 strains from other foci in the North Caspian and North Aral regions, isolated from 1912 to 2003. The phylogenetic analysis was performed drawing on the whole-genome SNP analysis, which was conducted on the basis of 2188 SNPs identified in the core genome using the Wombac 2.0 program. Maximum Likelihood Dendrogram (GTR model) was used for the analysis of phylogenetic relationships between strains. Results and discussion . All studied strains from the foci of the North Caspian region belong to the main subspecies (biovar medievalis) of the plague pathogen. These are highly virulent and epidemiologically dangerous strains. The whole-genome sequencing and phylogenetic analysis of 30 strains from the Volga-Ural sandy focus, as well as adjacent plague foci, reveal that the strains (biovar medievalis) of two phylogenetic branches - 2.MED4 and 2.MED1 - were spread across the focus under study in the early 20th century. It is confirmed that 2.MED1 strains were the etiological agents of plague outbreaks in the Volga-Ural sandy focus during this period. The study revealed the presence of parallel evolutionary lines in 2.MED1 associated with plague outbreaks in the first half of the last century. In the second half of the 20th and early 21st centuries, the modern evolutionary line of 2.MED1 became widespread in the Volga-Ural sandy focus. The strains of this line are closely grouped, which indicates their close genetic relationship. Only sporadic cases of plague were recorded during this period. Modern strains from the Volga-Ural sandy focus (1963-2003), as well as the strains previously isolated there (1912-1945), do not originate from each other. These strains represent closely related, independent evolutionary branches, extending from the common trunk of 2.MED1. Modern strains originating from those of the North Aral desert focus (1945) form a separate cluster in the dendrogram. This suggests that, following a break in the 1950s, the Volga-Ural sandy focus was recolonised by closely related strains from the North Aral region.

Crystal chemistry of halurgite, Mg4[B8O13(OH)2]2·7H2O, a microporous heterophylloborate mineral

AbstractThree samples of halurgite were re-examined: two from the Chelkar salt dome in the North Caspian Region, Western Kazakhstan (the type locality and including the type specimen), and one from a new locality in the Satimola salt dome located in the same region. The crystal structure of halurgite has been solved for the first time on the specimen from Chelkar with the empirical formula Mg3.94[B8.03O13.03(OH)1.97]2·7.16H2O; refinement began with single-crystal X-ray diffraction data and was subsequently refined on a powder sample using the Rietveld method (Rp= 0.0232,Rwp= 0.0354 andRobs= 0.0558). The idealised crystal chemical formula of halurgite is Mg4[B8O13(OH)2]2·7H2O. The mineral is monoclinic,P2/c,a= 13.201(2),b= 7.5622(10),c= 13.185(2) Å, β = 91.834(14)°,V= 1315.6(4) Å3andZ= 2. The crystal structure is unique. Eight B polyhedra form a fundamental building block [B8O16(OH)2], which is a six-membered borate ring (built by two pairs of B tetrahedra and two B triangles) with two additional triangular BO2(OH) groups. Each [B8O16(OH)2] ring is linked to six adjacent analogous rings to form a [B8O13(OH)2]∞layer. These layers are connectedviaMgO6and Mg(OH)2(H2O)4octahedra into a microporous heteropolyhedral pseudo-framework. The crystal structure of halurgite can also be described in terms of an approach developed for heterophyllosilicates containing three-layerHOHmodules, whereHOHrefers to an octahedral layerOsandwiched between two heteropolyhedral layersH. In halurgite theHOHmodule consists of two heteropolyhedral (BO3triangles + BO4tetrahedra) borateHlayers [B8O13(OH)2]∞and a central interruptedOlayer composed of MgO6octahedra, whereas a more voluminous Mg(OH)2(H2O)4octahedral complex and additional H2O molecules are located betweenHOHmodules. Halurgite and four related synthetic H-free boratesM2Cd3B16O28andM2Ca3B16O28(M= Rb or Cs) can be considered microporous heterophylloborates.

The Akchagylian stage (late Pliocene-early Pleistocene) in the North Caspian region: Pollen evidence for vegetation and climate change in the Urals-Emba region

Samples from 12 drillhole-cores from the Urals-Emba region to the north-east of the Caspian Sea were analysed for pollen and spores. The records reveal vegetation and climate changes for the late Pliocene to early Pleistocene within the time interval from ca. 3.6 to ca. 1.65 Ma. According to the results of the pollen analysis, at the beginning of the Akchagylian stage (3.6–3.4 Ma) there was a cooling and change in structure of the dendroflora, and steppe-dominated landscapes were present. At the end of the early Akchagylian, and continuing into the middle Akchagylian, a maximum variety of pollen from tree species occurred. The presence of mesophilic and thermophilic elements signifies a moderately warm and humid climate occurred at around 3.2 Ma, probably related to the ‘Mid-Pliocene Warm Period’. A second major cooling occurred at around 2.5 Ma coinciding with the onset of northern hemisphere glaciations. During this time, coniferous forests dominated by Picea, Pinus and Abies with lesser numbers of broad-leaved trees were established. At the end of the Akchagylian, at around 1.8 Ma, the climate became more arid and steppe landscapes were re-established. During the Akchagylian, alternations between forest- and steppe-dominated landscapes occurred at least three times in the Urals-Emba region. Results are compared with pollen spectra in surface samples, and with ostracods and foraminiferal assemblages in cores from the study region.

Redefinition of satimolite

ABSTRACTThe borate mineral satimolite, which was first described in 1969 and remained poorly-studied until now, has been re-investigated (electron microprobe analysis, single-crystal and powder X-ray diffraction studies, crystal-structure determination, infrared spectroscopy) and redefined based on the novel data obtained for the holotype material from the Satimola salt dome and a recently found sample from the Chelkar salt dome, both in North Caspian Region, Western Kazakhstan. The revised idealized formula of satimolite is KNa2(Al5Mg2)[B12O18(OH)12](OH)6Cl4·4H2O (Z = 3). The mineral is trigonal, space group R$\bar{3}$m, unit-cell parameters are: a = 15.1431(8), c = 14.4558(14) Å and V = 2870.8(4) Å3 (Satimola) and a = 15.1406(4), c = 14.3794(9) Å and V = 2854.7(2) Å3 (Chelkar). The crystal system and unit-cell parameters are quite different from those reported previously. The crystal structure of the sample from Chelkar was solved based on single-crystal data (direct methods, R = 0.0814) and the structure of the holotype from Satimola was refined on a powder sample by the Rietveld method (Rp = 0.0563, Rwp = 0.0761 and Rall = 0.0667). The structure of satimolite is unique for minerals. It contains 12-membered borate rings [B12O18(OH)12] in which BO3 triangles alternate with BO2(OH)2 tetrahedra sharing common vertices, and octahedral clusters [M7O6(OH)18] with M = Al5Mg2 in the ideal case, with sharing of corners between rings and clusters to form a three-dimensional heteropolyhedral framework. Each borate ring is connected with six octahedral clusters: three under the ring and three over the ring. Large ellipsoidal cages in the framework host Na and K cations, Cl anions and H2O molecules.

First data on the radiocarbon age of the Atelian deposits in the North Caspian Region

This paper reports data on the Atelian horizon identified in the Caspian Sea bottom. Seismoacoustic profiling has made it possible to determine its area, position, and setting in the Upper Quaternary sequence and the relation to the host deposits. According to the drillhole core data, the Atelian horizon is composed of continental clay loam and sandy loam containing peatlike organic remains. They are depleted in biogenic residues containing rare freshwater mollusk species. The Atelian deposits were accumulated in lake reservoirs filling the depressions developed in the strata of the Upper Khazarian horizon. The radiocarbon age determined for the first time by humic acids has been used to estimate the Atelian deposition time in the range of 40 000–45 000 calibrated years BP.

Seismic hazard assessment for oil-and-gas-bearing shelf zones: A case study of the North Caspian region

Seismic hazard assessment is done for oil field areas in the North Caspian region by a method earlier successfully applied to other areas. The method involves general seismic zoning data, available regional databases on recurrence of seismic shaking, known models of ground motion attenuation in seismoactive regions, and data on geological and geophysical surveys in the studied area. The assigned level of seismic hazard of the region is refined using probabilistic analysis; additionally, disaggregation is made and accelerograms are synthesized (the latter are necessary for seismic microzoning of particular sites using the numerical nonlinear analysis of ground seismic response). The amplitude and spectral characteristics of ground motions are obtained which are necessary for seismic resistance design and construction of petroleum industry objects.

The problem of the neolithisation process chronology in Povolzhye

The Lower and Middle Volga basin regions border the Caucasus and Central Asia in the South. These regions are important in the study of the neolithisation process in Europe and the chronology of Neolithic cultures is of great significance in this respect. New 14C dates of different organic materials from archaeological sites in these regions have been obtained in the last five years. According to these data, the beginning of neolithisation in North Caspian region can be dated to the beginning of the 5th millennium BC; but in the Povolzhye it happened at least a millennium earlier.

Beetles of the superfamily Curculionoidea (Coleoptera) in a complex semi-desert in relation to climate changes in the North Caspian region

In desert and steppe habitats of the complex North Caspian semi-desert, more than twofold differences in the number of hortobiont Curculionoidea species (33 and 75 species, respectively) were observed between the “dry” (1972–1974) and “humid” (2003–2005) climatic phases. The abundance of most species changed. Polyphagous steppe weevils of the subfamily Entiminae (Otiorhynchus velutinus, Euidosomus acuminatus, Omias verruca, and O. rotundatus) with spring activity of adults were the most stable, representing the main dominants of the spring communities both in the 1970s and 2000s. Nearly all of the weevils that changed their abundance since the 1970s were specialized herbivores with summer adult activity. In the more humid 2000s, the abundance of some desert-steppe weevils dominating the desert communities (Phacephorus nebulosus, Metadonus anceps and especially Ptochus porcellus) dropped drastically. Most of the species whose abundance increased most strongly (Phyllobius brevis, Trachyphloeus amplithorax, Archaeophloeus inermis, Stenopterapion tenue, Sitona inops, S. longulus, Tychius spp.) are associated with Medicago romanica, the plant that considerably raised its density in the microdepressions during the “humid” phase. The data show an evident reduction of the most xerophilic (desertsteppe) components of the weevil community and an increase in the fraction of mesophilic species. These changes seem to follow a cyclic pattern.

Evolution of the Northern Caspian Sea Region and the Volga delta in the late Pleistocene-Holocene

On the basis of geologic-geomorphologic studies, an alternative concept regarding the evolution of the Northern Caspian Sea Region and the adjacent areas in the boundary of the Pleistocene-Holocene is presented. A supposition is made about the existence of a large lagoon in the North Caspian Region that the Volga River emptied into forming a delta. Later, water from the lagoon flowed as a “stratum” stream into the Black Sea through the Manych Strait. A conclusion is reached that the Baer mounds were formed on the bottom of this stream.

Quantitative characteristics of soil mesofauna in the semidesert solonetzic complex of the north Caspian region

The results of long-term quantitative assessments of the invertebrate populations inhabiting the soils of a clayey semidesert are analyzed. The dominant species in the different soils of a solonetzic soil complex are compared. The distribution patterns of the dominant groups of invertebrates in relation to the soil and vegetation complexity dictated by the clearly expressed microrelief are discussed. The changes in the populations of the soil invertebrates are considered against the background of changes in the precipitation during the growing season in different years. It is shown that the population density of the soil invertebrates varies within broad limits in all the soils of the complex. At the same time, it remains considerably lower in the solonchakous solonetzes of the microhighs in comparison with that in the soils of the slopes and microlows. The most contrasting differences in the species composition and the numbers of soil invertebrates are observed for the solonetzes of the microhighs and the meadow-chestnut soils of the microlows. This work was performed at the Dzhanybek Research Station of the Institute of Forestry of the Russian Academy of Sciences on the Volga-Ural interfluve (30 km to the north of Lake El’ton).

Paleogene biostratigraphy of the North Caspian region based on dinocysts and nannofossils from the Novouzensk borehole. Article 2: Biotic events and paleoecological settings

The relatively complete late Danian-initial Lutetian succession of biotic events, which are suitable to serve as biostratigraphic reference levels for interregional correlations are defined in the section of the Novouzensk reference borehole based on dinocyst and nannoplankton assemblages. The analysis of palynological and nannofossil assemblages allows dynamics of basin development and sea-level fluctuations to be traced. Three major stages reflecting different sedimentation regimes are established in the borehole section: (1) Danian with terrigenous-carbonate sedimentation regime corresponding to the Algai and Tsyganovka formations; (2) Selandian-Thanetian (initial Eocene included) characterized largely by siliceous-terrigenous sediments of the Syzran, Novouzensk, and, partly, Bostandyk formations; (3) Ypresian-Lutetian with the carbonate-terrigenous sedimentation regime corresponding to the upper part of the Ypresian Bostandyk and Lutetian Kopterek formations. The composition of dinoflagellate and nannoplankton assemblages characterizes the North Caspian basin as an internal largely shallow sea with a changeable temperature regime. The paleoecological analysis of phytocoenoses made it possible to define basin fluctuations comparable with third-order rhythms. Four Danian rhythms definable in the Algai and Tsyganovka formations indicate conditions of an open warm-water basin. Dynamics of the step-wise shoaling of the basin was characteristic of the Selandian-early Thanetian ages with subsequent restoration of the marine regime in the late Thanetian. The Syzran Formation corresponds to two Selandian rhythms, which were formed in shallower settings of the restricted sea basin. Four Thanetian rhythms are established in the Novouzensk Formation. The early Thanetian basin was characterized by the shallowest disturbed marine conditions, which were followed by the restored normal marine regime in the late Thanetian. Six Ypresian rhythms correspond to the Bostandyk Formation (Yp-0, Yp-1, Yp-5-Yp-8) reflecting transition from initial Ypresian coastal (Yp-0, Yp-1) to normal marine conditions during the Yp-5 rhythm. The early (Yp-2-Yp-4) and late (Yp-9-Yp-10) Ypresian corresponded to the sedimentation break. Most abundant and diverse microbiotic assemblages characteristic of the Yp-7 rhythm are correlative with the EECO event. The marly Kopterek Formation corresponding to the early Lutetian rhythm (Lu-1) is characterized by diverse thermophilic biota.

NEW DATA ON RADIOCARBON CHRONOLOGY OF NEOLITHIC CERAMICS FROM THE VOLGA-KAMA REGION

The present article outlays a chronological sequence based on radiocarbon dating using ceramics from Neolithic sites in the Volga-Kama region. Sites in the North Caspian region are considered the most ancient being dated to the first half of the 6th millennium BC. The Neolithic culture of the southern forest-steppe zone of the Volga-Ural interfluve was formed at approximately the same time. Neolithic sites in the Lower Volga region are considered slightly later dating to the second half of the 6th millennium BC. Contacts between the steppe and forest-steppe cultures of the Middle Volga led to the emergence of the pricked decorative style in ceramics in the early 5th millennium BC. This tradition survived until the early 4th millennium BC. In the mid 5th millennium BC, the comb-cogged stamp decorative element emerged in the forest-steppe zone of the eastern Volga and in the forest zone of the Volga-Kama region. In southern areas, this tradition continued until the mid 4th millennium BC, and in northern areas, until the late 4th millennium BC.