فهرست مطالب

International Journal of Science
Volume:2 Issue: 2, 2001

  • تاریخ انتشار: 1380/10/11
  • تعداد عناوین: 4
|
  • Dinocyst Morphotype Groups Versus Sequence Stratigraphy of the Upper Jurassic Sediments of the Northern Switzerland Sedimentary Basin
    Ebrahim Ghasemi, Nejad Page 1
    Variations in ratios of chorate (C) dinoflagellate cysts to proximochorate (P), proximate (P) and cavate (C) forms recovered from the Rhodano-Swabian sedimentary basin in northern Switzerland have been correlated with sequence boundaries and sedimentary cycles established for this basin. The variations in these ratios and abrupt increases and decreases in the number of recorded species from the same strata corroborate closely the sequence boundaries established by Gygi et al., (1998) using other parameters such as lithology and macrofossil content of the sediments. Highstands of sea level aremarked by an abrupt increase in species diversity and in C: PPC ratio. In contrast, lowstands are indicated by rapid decline in the abundance of species and a decrease in C: PPC ratios.
  • Contra-?t-Continuous Functions between Topological Spaces
    Saeid Jafari Page 2
    In this paper, we apply the notion of a-open sets in topological spacesto present and study contra-a-continuity as a new generalization of contra-continuity (Dontchev, 1996).
  • Palynostratigraphy and Palaeobiogeography of a Lower Palaeozoic Sequence in the Type-Section of Shirgesht Formation, Northern Tabas City, East-Central Iran
    Hussein Mehrjerdi Page 3
    This study was carried out to the southern part of the Derenjal mountains, some ten kilometers north of Shirgesht village in East-Central Iran. Stratigraphy of Derenjal, Shirgesht and Niur localities indicate some Lower Palaeozoic rock units in these areas. Among the above-mentioned rock units, the uppermost part of Derenjal Formation, Shirgesht Formation and Niur Formation were studied from palynological point of view. Forthis purpose the upper part of the Derenjal, Shirgesht and Niur formationswere systematically measured and sampled. Based on appearance and disappearance of the identified palynomorph taxa, six acritarch biozones were established. Biozone-I appears in the uppermost part of the Derenjal Formation and lowermost ShirgeshtFormation, and suggests the uppermost Cambrian to lowermost Tremadocian age.Biozones II through V occur in the Shirgesht Formation, representing the Tremadocian to Llanvirnian age. Biozone VI appears in the Niur Formation and suggests an early Silurian age for this Formation. Therefore, there is a major "hiatus" within the Lower Palaeozoic sequence in the studied area. This appears between the Shirgesht and Niurformations and includes the upper Ordovician strata. This hiatus possibly corresponds to the Caledonian Orogeny. In this study a palynological zonation has been established andcompared with those of the other parts of the world. The comparison reveals that East-Central Iran has been a part of the Mediterranean acritarch province during the Early/Middle Ordovician age.
  • Freshwater Gastropod of Khuzestan Province, South-West Iran
    Allahbedasht Mansoorian Page 4
    Many freshwater gastropodes are involved in the life cycle of parasitic flukes. Some of these are important in public heath and veterinary medicine. A comprehensive snail search was undertaken throughout provinces in Iran. In the first step, freshwater bodies of Khuzestan, were searched for potential intermediate host snails. Fifteen taxa,namely 8 prosobranch snails and 7 pulmonate snails were collected during the 1990s. Neritina mesopotamica Martens 1879 was found to be new species for Khuzestan.