چكيده لاتين :
The Cenozoic outcrops are significantly widespread around the Rafsanjan city, southeastern Iran which conforming a volcano-sedimentary complex. Volcanic rocks belong to Urumieh-Dokhtar Magmatic Belt (Fig. 1) and consist of basaltic andesite, basalt, and pyroclastic deposits. Sedimentary rocks are composed of Marl, fossiliferous limestone, conglomerate and sandstone. Although sedimentary deposits have a good spread in the area, no comprehensive study has been conducted on these deposits so far and most of the previous studies were devoted to igneous rocks (e.g., Rahmanian and Ahmadipour, 2010, 2013). The present study discusses the biostratigraphic framework of the Paleocene- Early Eocene deposits in the Kuh–e-Ketabi section (west of Rafsanjan The Kuh–e-Ketabi section is situated about 22 km, west of Rafsanjan (Kerman Province; Fig. 1). Systematically sampling for the foraminifera study was performed from all 161 m of the Kuh-e- Ketabi section. The samples consist of marls, dolostones, sandstones, and limestones. Planktonic and benthonic foraminifera were studied in thin sections for lithified samples. The standard washing method was applied for samples of relatively soft lithologies (i.e., marl) to obtain washed residues. The samples were washed through 500μm to 88μm sieves. However, the results were not satisfactory, owing to a lack of fossils. Foraminifera observed in the thin section were studied and photographed digitally under transmitted-light (Optika T3. 15A) and binocular microscopes. For biostratigraphic determination, the biozonation scheme of wade et al., 2011 and the SBZ scheme of Serra-Kiel et al. (1998) have been adopted for planktonic and benthic foraminifera, respectively.
3-Results and discussion
3-1-Biostratigraphy
Study of the Palaeocene-Early Eocene depositional microfossils in the Kuh-e-Ketabi section, revealed 16 genera and species of Planktonic foraminifera and 24 genera and species of benthonic foraminifera (Fig. 2). The identified foraminifera fall into the following categories: LBF, smaller benthic foraminifera, and pelagic foraminifera. From base to top, three foraminiferal assemblages were determined in the study area.
Assemblage A: This assemblage begins at the basal part of the section and extends upward with a thickness of 62 m. This assemblage is dominated by planktonic foraminifera. The most important fauna are Morozovella subbotinae, Morozovella angulata Globanomalina chapmani, G. ehrenbergi, Parasubbotina pseudobulloides, P. variospira, Globoconusa daubjergensis, Subbotina triloculinoides, S. inaquispira, S. trivialis, Parvularugoglobigerina sp., Igorina cf. tadjikistanensis, Morozovella sp., M. apanthesma, Acarinina sp. According to the Biostratigraphic interval between the Lowest Occurrence (LO) of Morozovella angulate and LO of Morozovella subbotinae, the the Morozovella angulata Lowest occurrence zone (P3) of wade Biozonation (Wade et al., 2011) has been determined in this interval. This zone ranges in age from late early to middle Paleocene.
Assemblage B: This assemblage was recorded from 62 to 70.4 m. This assemblage is characterized by the co-occurrence of both benthic and planktonic foraminifera. Benthic foraminifera were dominated by Miscellanea miscella, Idalina sinjarica, Kathina selveri, Ranikothalia sindensis, Discocyclina ranikotensis, Operculina subsalsa, O. patalensis, and Dictyokathina simplex. This fauna is associated with coralline algae e. g. Distichoplax biserialis. This fauna is correlative with SBZ4 Biozone. (1998). It indicates a Late Paleocene (Thanetian) age. According to Serra-Kiel et al. (1998), the first occurrence of R. sindensis and Dictyokathina simplex has been recorded from the base of Biozone SBZ4 in the Tethyan paltform. However, the biostratigraphic range of R. sindensis has been recorded from Late Paleocene to Early Eocene, the co-occurrence of this species with the commonly occurring Paleocene assemblage of Miscellanea miscella and Kathina selveri indicates Thanetian age. The R. sindensis appears to be abundant in the Lower Eocene rocks and rare in the Upper Paleocene facies, corresponding to the reported specimens of the Sistan area (Babazadeh, 2011). Also, the fauna association of this biozone corresponds to the biozone no. 43 introduced by Wynd (1965). Other associated species in this zone include Assilina sp., Ranikothalia sahni, Operculina salsa, Caskinon rajkae, Discocyclina sp., Lockhartia haimei, L. conditi, Subbotina sp. Planktonic foraminifera were dominated by Subbotina triloconoides, Morozovella sp., Globanomalina chapmani. Parasubbotina pseudobulloides.
There is an interval (12m thick) between the assemblage B and C which is composed of nonfossiliferous, highly tectonized dolomites and red-colored marls. The extensive of these layers is likely to reflect periodical desiccation of shallow-marine to hypersaline lagoons during the latest Paleocene. The boundary between Paleocene and Eocene is probably located in this unit.
