伊朗中伊朗盆地库姆组地层的时代

对伊朗中伊朗盆地卡尚地区库姆组的微体化石样品分析 ,不仅发现了新的有孔虫和介形虫化石组合 ,而且还首次发现了较丰富的钙质超微及少量的沟鞭藻化石。依据这些化石的组合面貌 ,认为库姆组含始新世地层无疑 ,修正了以往认为库姆组地层时代为中—晚渐新世至早中新世的观点。

AGE OF THE QOM FORMATION IN THE CENTRAL IRANIAN BASIN,IRAN

The Kashan Block is located in southeast of the Central Iranian Basin, Iran.The Qom Formation is the main objective beds for oil and gas exploration of the basin, thus, correct age determination of the Formation is of great significance.The analyses of the samples of the microfossils from the Qom Formation show that there are not only rather abundant calcareous nannofossils and a small number of dinoflagellates, but also new fossil benthonic foraminifers and ostracods. Calcareous nannofossils and dinoflagellates first reported from this Formation are Cyclicargolithus floridanus, C.abisectus, Dictyococcites bisectus, D. scrippsae, Coccolithus pelagicus, Sphenolithus dissimilis, S. moriformis, Reticulofenestra minute, Helicosphaera euphratis etc., and dinoflagellates including Homotryblium plectilum, Thalassiphora pelagica, Hystrichokolpoma rigaudiae, Operculodinium centrocarpum, Spiniferites pseudofurcatus, Palaeocystodinium golzowense etc. Benthonic foraminifers are Nummulites aff. variolarius, Operculina canalifera, O. sp., Assilina aff. spira, Orbitolites sp., Discocyclina sp., Neodiscocyclina cf. barkeri etc.. Ostracods include Cytheridea cf. scruposa,C. cf bundensis, C. sp., Krithe oryza, K. cf. pernoides, Cytherella virgulata, C. jonesiana, Alocopocythere dhansariensis, Xestoleberis sp., Propontocypris sp., Paracypris sp., Loxoconcha sp., Hermanites cf. grafica, Eopaijenborchella sp., Krithe cf. pernoides, Bairdia montiformis, Propontocypris zongbuensis, P. sp.etc. The present fossils show that the Qom Formation can be undoubtedly attributed to Eocene,most probably the Middle Eocene sediments.