چكيده لاتين :
Introduction
The Qom Formation consisting of limestones, marine marls, gypsum and siliciclastics (Reuter et al., 2009) was deposited at the last sea transgression in the Oligo-Miocene age (Khaksar & Maghfouri–Moghadam, 2007; Mohammadi et al., 2011, 2015; Mohammadi & Ameri, 2015) with northwest-southeast trending in three basins of Sanandaj-Sirjan fore-arc, Urumieh-Dokhtar intra-arc and Central Iran back-arc (Mohammadi et al., 2011; 2015; 2018; Mohammadi & Ameri, 2015). Due to the hydrocarbon resources and communicative role between Eastern and Western Tethys, the region the study of Qom Formation has been considered by many researchers (Mohammadi et al., 2018; Mohammadi & Ameri, 2015). This Formation was deposited at the north-eastern coast of the Tethyan Seaway (Reuter et al., 2009; Mohammadi et al., 2015). The Transgression of the Tethyan Seaway in the Iranian Plate started from the southeast and continued northwestward gradually (Mohammadi et al., 2013). Concerning the opening and closure times of the Tethyan Seaway on Iranian Plate, different views have been presented ranging from Early Oligocene (Rupelian) to Middle Miocene (Langhian) by Bozorgnia (1966), Schuster & Wielandt (1999), Berning et al. (2009), Reuter et al. (2009), Harzhauser et al. (2007), Bassi et al. (2009), and Khaksar & and Maghfouri Moghadam (2007). Due to the study of more than 100 stratigraphic sections of the Qom Formation and more than 30 geological maps of different parts of Iran (more than 1700 km of the north-eastern seashore of the Tethyan Seaway), Mohammadi et al. (2013) believed the opening time of the Tethyan Seaway on Iranian Plate began at 34°2´ latitude with the age of Rupelian, 35° latitude to the Chattian age and latitude greater than 35° to the Miocene.
Materials and Methods
In this research, seven marl, and thirty two calcareous samples were collected from Gonjan section, east of Rabor.
Discussion
Qom Formation in the study area has 100 meters in thickness and consists of five limestone and marl informal members that these informal members are lower limestone, lower marl, middle limestone, upper marl, and upper limestone. Qom Formation in the study area lay on top of the Eocene volcanic rocks and the upper boundary is covered by recent alluvium. The following 41 species and 30 genera of foraminifera from the Gonjan stratigraphical section are identified: Triloculina trigonula, Discorbis sp., Chilostomella sp., Planorbulina sp., Pyrgo sp., Operculina sp., Haplophragmium slingeri, Valvulina sp., Sphaerogypsina sp., Amphistegina sp., Miliolids., Operculina camplanata, Elphidium sp., Textularia sp., Heterostegina sp., Eulepidina sp,. Nephrolepidina tournoueri, Nephrolepidina sp., Cibicides sp., Eulepidina cf. dilatata, Meandropsina iranica, Rupertina sp., Heterostegina cf. costata, Eulepidina cf. elephantina, Asterigerina rotula, Sphaerogypsina globulus, Rotalia viennotti, Uvigerina mioza, Uvigerina costata, Uvigerina sp., Amphistegina lobifera, Ammonia sp., Amphistegina hauerina, Rotalia sp., Quinqueloculina sp., Gyroidina sp., Lenticulina mamailligera, Nonion tuberculatum, Bolivina cf. churchi, Heronallenia kempii, Melonis simplex, Anomalinoides globulosa.
Based on the diversity of the identified foraminifera in this section and also absence Nummulites fichteli, Nummulites intermedius and Nummulites vascus (index of Rupelian), Miogypsina (index of late Chattian-Aquitanian), Borelis melo curdica (index of the lower boundary of Burdigalian) and Abundance of lepidocyclinids, that suggested the age of Qom Formation deposits in Gonjan section is Rupelian?-Chattian. The presence and abundance of larger benthic foraminifera (such as Lepidocyclinids, Operculina, Heterostegina, Amphistegina), Coralline red algae and Coral fragments indicate the oligophotic to mesophotic and oligotrophic to mesotrophic conditions in the tropical to subtropical environments with normal salinity and low to high energy during the deposition of the Qom Formation.
Acknowledgment
The authors are grateful to Prof. Davide Bassi University of Ferara (Italy), Dr. Ebrahim Mohammadi, Dr. Mohammad Javad Hassani (Department of Ecology, Institute of Science and High Technology and Environmental Sciences), Dr. Mohammad Allahkarampour Dill (National Iranian South Oil Company), Dr. Mehdi Ghaedi, Dr. Zohreh Khosrawi, Mrs. Sara Seyfi, Mrs. Sahar Aflaki, Mr. Sajjad Shamsedini, Mr. Mehran Mashayekhi, Mr. Omid Jahed, Mr. Reza Afroz, Mr. Ali Binazadeh for their useful discussions.
