PHÁT HIỆN MỚI VỀ HÓA THẠCH STROMATOLIT TRONG TRẦM TÍCH HỆ TẦNG RINH CHÙA, TRŨNG NA DƯƠNG, LẠNG SƠN

THÔNG BÁO KHOA HỌ

Impact of historical founder effects and a recent bottleneck on MHC variability in Commander Arctic foxes (Vulpes lagopus)

Populations of Arctic foxes (Vulpes lagopus) have been isolated on two of the Commander Islands (Bering and Mednyi) from the circumpolar distributed mainland population since the Pleistocene. In 1970–1980, an epizootic outbreak of mange caused a severe population decline on Mednyi Island. Genes of the major histocompatibility complex (MHC) play a primary role in infectious disease resistance. The main objectives of our study were to compare contemporary variation of MHC class II in mainland and island Arctic foxes, and to document the effects of the isolation and the recent bottleneck on MHC polymorphism by analyzing samples from historical and contemporary Arctic foxes. In 184 individuals, we found 25 unique MHC class II DRB and DQB alleles, and identified evidence of balancing selection maintaining allelic lineages over time at both loci. Twenty different MHC alleles were observed in mainland foxes and eight in Bering Island foxes. The historical Mednyi population contained five alleles and all contemporary individuals were monomorphic at both DRB and DQB. Our data indicate that despite positive and diversifying selection leading to elevated rates of amino acid replacement in functionally important antigen-binding sites, below a certain population size, balancing selection may not be strong enough to maintain genetic diversity in functionally important genes. This may have important fitness consequences and might explain the high pathogen susceptibility in some island populations. This is the first study that compares MHC diversity before and after a bottleneck in a wild canid population using DNA from museum samples

Spectral reflectance properties of zeolites and remote sensing implications

The 0.3- to 26-μm reflectance spectra of a suite of 28 zeolites were measured and analyzed to derive spectral-compositional-structural relationships. Below ~7 μm, the spectra are largely dominated by absorption features associated with zeolitic water. At longer wavelengths, the spectra are dominated by absorption features associated with the aluminosilicate framework. The spectra exhibit a number of systematic variations which can be used for both structurl and compositional determinations. These include: (1) distinguishing different structural groups on the basis of wavelength position variations associated with absorption features in the 8.5- to 26-μm region that are related to differences in the structure of the aluminosilicate framework; (2) determining the major cation which is present (Ca, Na, K) and the associated electronic environment of the zeolitic water on the basis of how these cations hydrogen bond to the water molecules in the void spaces and consequently affect water-related absorption band positions, particularly in the 1.4, 1.9, and 2.0- to 2.5-μm regions; (3) determining the Al:(Al + Si) ratio and SCFM chemical index on the basis of absorption features in the 7- to 26-μm region which are most sensitive to these compositional variations; and (4) identifying ironbearing zeolites on the basis of absorption features in the 0.35- to 0.9-μm region. The wavelength position and number of H2O-associated absorption bands are sensitive to factors such as the type of major cation, degree of hydrogen bonding, and size of the void space, all of which are somewhat interrelated.This study was supported by a research grant from the Natural Sciences and Engineering Research Council of Canada, a contract from the Canadian Space Agency Space Science Program, a discretionary grant from the University of Winnipeg (to E.A.C.), and the Louise McBee Scholarship of the Georgia Association for Women in Education, University of Georgia (to P.M.A.).This study was supported by a research grant from the Natural Sciences and Engineering Research Council of Canada, a contract from the Canadian Space Agency Space Science Program, a discretionary grant from the University of Winnipeg (to E.A.C.), and the Louise McBee Scholarship of the Georgia Association for Women in Education, University of Georgia (to P.M.A.).https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2000JE00146

Glauconitic bryozoan shells in shelf sediments of Western Kamchatka

© 2017, Pleiades Publishing, Inc. Glauconite segregations in Oligocene–Miocene shelf sediments of Western Kamchatka (Kakert and Gakkha horizons) are studied. Glauconite occurs in the studied samples as morphologically different grains, finely dispersed cement, and pseudomorphoses after organogenic structures (siliceous sponge spicules, diatom algae frustules, and others). In addition, samples of the clasts of bryozoans, volcanic glass, and terrigenous grains revealed for the first time traces of the boring algae similar to recent species of genus Hyella and, possibly, Dalmatella, whose tubules are sometimes filled with the finely dispersed glauconite. Our data based on the detailed petrographic studies and SEM investigations confirm and supplement the opinion of several researchers about an important role of microbiota on the glauconite formation. The paper discusses different stages of the glauconite formation in sediments of the Kakert and Gakkha horizons and the possible setting of glauconite infilling in the algal borer trails and holes

Glauconitic bryozoan shells in shelf sediments of Western Kamchatka

© 2017, Pleiades Publishing, Inc. Glauconite segregations in Oligocene–Miocene shelf sediments of Western Kamchatka (Kakert and Gakkha horizons) are studied. Glauconite occurs in the studied samples as morphologically different grains, finely dispersed cement, and pseudomorphoses after organogenic structures (siliceous sponge spicules, diatom algae frustules, and others). In addition, samples of the clasts of bryozoans, volcanic glass, and terrigenous grains revealed for the first time traces of the boring algae similar to recent species of genus Hyella and, possibly, Dalmatella, whose tubules are sometimes filled with the finely dispersed glauconite. Our data based on the detailed petrographic studies and SEM investigations confirm and supplement the opinion of several researchers about an important role of microbiota on the glauconite formation. The paper discusses different stages of the glauconite formation in sediments of the Kakert and Gakkha horizons and the possible setting of glauconite infilling in the algal borer trails and holes

Distribution of polycyclic aromatic hydrocarbons in eolian and eolian-deluvial sediments from the North Iceland

This work considers results of a study of Holocene cover sediments in Iceland. They are largely composed of wind-transported palagonitized hyaloclastite particles and coeval horizons of acid and basic tephras. It is established that polyciclic aromatic hydrocarbons (PAH) are released from basaltic glass in natural environments only in case of intense physicochemical alteration and destruction of its structure. This process does not influence PAH composition and their quantitative proportions. No new PAH formed during several thousands of years in Holocene section. Hydrocarbons are transferred from fixed state in basaltic glass into free state in palagonites practically without any changes. PAH were mainly redeposited by winds, derived together with palagonite from weathered hyaloclastites, and precipitated from atmosphere with tephra during eruptions