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    Wyświetlanie 1-3 z 3
    Tytuł:
    Unraveling cementation environment and patterns of Holocene beachrocks in the Arabian Gulf and the Gulf of Aqaba : stable isotope approach
    Autorzy:
    Koeshidayatullah, A.
    Al-Ramadan, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059746.pdf
    Data publikacji:
    2014
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    cementation
    beachrocks
    stable isotope
    Arabian Gulf
    Gulf of Aqaba
    Opis:
    This paper analyses Holocene beachrocks from the Arabian Gulf and the Gulf of Aqaba to explain the mechanisms that influence the cementation process in these areas. Holocene beachrocks in the Gulf of Aqaba are composed of predominantly terrigenous material derived from erosion of adjacent uplifted Precambrian basement, while the beachrocks in the Arabian Gulf are composed mainly of marine bioclasts and wind-blown siliciclastic sands. The cements of beachrocks in both areas show three textural varieties: (1) isopachous phreatic acicular aragonite; (2) a micritic envelope of high-Mg calcite (HMC); (3) meniscus and gravitational vadose HMC. Radiocarbon dating of beachrock samples from the Arabian Gulf yielded ages from ca. 2300 to 660 yr cal BP whereas samples from the Gulf of Aqaba range in age between 5500 and 2800 yr cal BP. Oxygen isotope values range from 2.6 to 4.4‰ respectively for the Arabian Gulf whereas the Gulf of Aqaba values range from 1.2 to 1.5‰. Carbon isotope values range from 3.2 to 5.9‰ for the Arabian Gulf whereas those from the Gulf of Aqaba range from 3.8 to 4.6‰. The values of δ18OVPDB and δ13CVPDB in the beachrocks of both areas suggest a marine origin. The beachrocks of the Arabian Gulf were precipitated under high evaporation conditions, while beachrocks from the Gulf of Aqaba were precipitated in normal shallow-marine conditions. The mineralogy and textural habits suggest that cementation of these beachrocks started within the shallow-marine phreatic zone.
    Źródło:
    Geological Quarterly; 2014, 58, 2; 207--216
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Formation conditions and diagenetic evolution of Sand Roses in clastic sabkhas along the Arabian Gulf Coastal Region, Eastern Saudi Arabia
    Autorzy:
    Al-Hussaini, A.
    Koeshidayatullah, A.
    Al-Ramadan, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059800.pdf
    Data publikacji:
    2015
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    sand roses
    desert
    diagenesis
    gypsum
    Arabian Gulf
    Opis:
    This field, petrographic and geochemical study aims at constraining the formation and diagenetic evolution of sand roses (desert roses) in interdune sabkhas in Eastern Saudi Arabia. These “roses”, which are mainly cemented by gypsum, carbonate, and clay minerals, occur as disc-shaped and spherical flower-like crystals. Sands, within the sand roses, are moderately-sorted, medium-grained, and sub-arkosic. Gypsum typically exceeds 20% of the volume of the roses, and locally gypsum is partly transformed to anhydrite. In addition to gypsum and anhydrite, early diagenetic modifications include precipitation of grain coating clay, dissolution of unstable grains (e.g., feldspar grains), and weak mechanical compaction. Iron oxide cement was formed when the sand roses exposed to the surface. The XRD and petrographic data indicate an increase in amounts of gypsum cement from the water table upward towards the sabkha surface. The sand roses also are larger and lighter in colour away from the water table. This study is expected to provide a better understanding of the mode of sand roses formation in the interdunes areas, as well as the diagenetic alterations in both phreatic and vadose zones.
    Źródło:
    Geological Quarterly; 2015, 59, 1; 71--78
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Seasonal variations, environmental parameters, and standing crop assessment of benthic foraminifera in eastern Bahrain, Arabian Gulf
    Autorzy:
    Arslan, M.
    Kaminski, M. A.
    Tawabini, B. S.
    Ilyas, M.
    Babalola, L. O.
    Frontalini, F.
    Powiązania:
    https://bibliotekanauki.pl/articles/2060170.pdf
    Data publikacji:
    2016
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Arabian/Persian Gulf
    benthic foraminifera
    standing crop
    eastern Bahrain
    Opis:
    Living benthic foraminifera in a relatively unpolluted site offshore Bahrain in the Arabian Gulf, were studied to determine the seasonal variability of their populations, as well as environmental parameters that may affect their distribution. The maximum foraminiferal density was observed during winter with the assemblages primarily dominated by rotaliids and secondarily by miliolids. The high population is attributed to an increased number of juveniles. A relationship between sediment grain size and the foraminiferal density reveals that juveniles were most abundant on coarse-grained sandy substrate and less abundant on fine-grained substrates. In spring, the foraminiferal density decreased, and the lowest values were observed during summer. The population increased again in autumn with highest juvenile/adult ratios. Moreover, results of relative abundance and species consistency show that Ammonia and Glabratellina are consistent from the shallowest to the deepest station, whereas miliolids occurred only at deeper stations. The numbers of peneroplidae and Elphidium also increased along the depth transect. Environmental characterization reveals that although the site is subject to eutrophication caused by nitrates and sulfates, pollution caused by hydrocarbons and heavy metals is not significant. The assessment of 63 heavy metals showed that none of the metals had concentrations that exceed internationally accepted norms [the devised level of Effect Range-Low], but with high concentration of strontium. The lack of a significant environmental effect of heavy metals is confirmed by the Foraminiferal Abnormality Index of <2%. Likewise, no hydrocarbon contamination was detected in the water or sediment samples. We conclude that the site in Bahrain is not yet adversely affected by human development, and therefore can provide baseline information for future comparison and assessment of foraminiferal assemblages in contaminated zones of the Arabian Gulf.
    Źródło:
    Geological Quarterly; 2016, 60, 1; 26--37
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-3 z 3

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