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The Gurpi Formation was measured and sampled in a stratigraphic section located on the northern limb of the Chenareh anticline to the north of Andimeshk. The thickness of the Gurpi Formation in this section is 288.5 meters and its lower boundary with the Ilam Formation is abrupt while its upper boundary with purple shales of the Pabdeh Formation is gradual and continuous. Paleontological studies led to the identification of 67 species belonging to 45 genera from 20 families of calcareous nannofossils, which made it possible to recognize CC18 to CC26 biozones from Sissingh standard classification scheme and NP1 to NP5 biozones from Martini standard classification scheme equivalent to biozones CNP1 to CNP7 from Agnini et al.. Based on the identified biozones, the duration of deposition of the Gurpi Formation was determined to be early Campanian–Selandian. In this section, the Emam Hassan Limestone Member was recognized with a thickness of 112.8 meters having been deposited during the early Maastrichtian. Both the lower and the upper boundaries of the Emam Hassan Limestone Member within the Gurpi Formation are continuous and gradual. The position of the Campanian–Maastrichtian, Maastrichtian–Danian (Cretaceous–Paleogene) and Danian–Selandian transitions in the Gurpi Formation were also determined in the studied section.

A conformable passage between Sarvak and Surgah Formations in Lurestan sedimentary basin reveals the potential of studying the Turonian–Coniacian boundary within Surgah Formation. Two sections of the Surgah Formation at Posht-e-Jangal and Pasan anticlines situated on the southeast of the Lurestan sedimentary basin have been studied on the basis calcareous nannofossils, and based on the observed distribution of nannoflora, the presence of CC12 to CC16 nannofossil biozones is documented which points to the latest Turonian to Coniacian age for the base of this Formation, while the top boundary is estimated approximately at earliest Santonian. Due to the absence of Micula staurophora, however, separation of CC13 and CC14 biozones is not possible and therefore, the Turonian–Coniacian boundary is placed somewhere within the said undivided interval. The FO of Calculites obscurus as the marker event for the top of CC16 biozone is not identified but on the basis of suspected LO of Lithastrinus septenarius as the marker event of the top of UC11 and onset of UC12, the record of early Santonian beds seems probable.

The Kopet-Dagh Basin is located in the northeast of Iran, extended over Iran, Turkmenistan, and Afghanistan with a west-northwest to east-southeast trend. The Iranian part of the basin is located between 61°14ˊ and 54°00ˊE and 38°16ˊ and 36°00ˊ N. Cretaceous successions are thick and well exposed in the northeast of Iran. The Cretaceous Ammonites are studied by Seyed-Emami (1980), Seyed-Emami & Aryai (1981), Seyed-Emami et al. (1984), Immel et al. (1997), Raisossadat (2004, 2006), Mosavinia et al. (2007, 2014), and Mosavinia & Wilmsen (2011). Calcareous nannoplankton biostratigraphy of Aitamir formation is studied by Susani (2005) and Hadavi & Musazadeh (2005).

The studied section, the Amirabad section, is located at a distance of 65 km to the northeast of Mashhad city, on the Mashhad-Kalat road (coordinates: N36°34ˊ59˝ and E60°09ˊ24˝; altitude: 720 m). Aitamir Formation is measured 668 m in this section and comprised siltstones, fossiliferous (bivalve and ammonite) sandstones, glauconitic sandstones, dark gray to greenish-gray silty shales, and dark gray shales. It conformably overlies the Sanganeh Formation and is overlain by the Abderaz Formation. A total of 139 samples were collected from the section at intervals 3-5 m to study the calcareous nannofossils. In addition, 40 m part of the topmost of the underlying Sanganeh Formation as well as the lowermost of the overlying Abderaz Formation were also measured and sampled. For nannofossil biostratigraphic investigations, all samples were processed using the gravity settling technique (Bown & Young, 1998). The prepared slides were observed under a Nikon Optiphot II Pol light microscope with a magnification ×1000. Bibliographic references for the calcareous nannofossils are given in Perch-Nielsen (1985), Varol (1992), and Burnett (1998). Ammonite samples were collected across the section and named and photographed at the paleontology laboratory of the Payam-e-Noor University of Mashhad. 

Nannofossil bioevents have been utilized to biostratigraphically classify the exposed sedimentary succession based on the CC biozonation scheme of Sissingh (1977, modified by Perch-Nielsen, 1985) and the NC biozonation scheme of Roth (1978, modified by Bralower et al., 1995). The biozones CC8 to CC10 and NC9 to NC13 were determined, and accordingly, the Aitamir Formation is attributed to Albian to late Cenomanian time interval. The lithology of sandstones and siltstones at the lower part of the Aitamir Formation influenced the preservation of nannofossil taxa. In this part, the Ammonite biozones have covered the gap of nannofossil biozones. The upper part of Leymeriella tardefurcata, Hoplites dentatus, Euhoplites loricatus, Euhoplites lautus Mortoniceras (M.) inflatum, Stoliczkaia dispar, Mantelliceras mantelli, Mantelliceras dixoni, Cunningtoniceras inerme and Acanthoceras rhotomagense biozones were determined at the Aitamir Formation except for the upper 20 meters, which contains no ammonite sample. Based on Ammonite biozones, the age of Late Early Albian to Middle Cenomanian is attributed to the Aitamir Formation.

The Gurpi Formation at Anaran Anticline in SE of Lurestan province.consists of 269.5 meters of marl with intercalation of limy marl; two formal members of Seymareh limestone and Emam-Hasan argillaceous limestone are also exposed. Studies reveal presence of 70 species belonging to 38 genera of calcareous nannofossils based on which 8 global biozones were differentiated. Consequently, the Gurpi Formation was attributed to middle Campanian through Paleocene. There is a distinct hiatus in Cretaceous-Paleogene boundary based on paleontological evidence, as deduced from the absence of nannofossil biozones NP1-NP4. It seems that the reactivation of Anaran linement as paleohigh caused facies changes and hiatus in Gurpi Formation in SE of Lurestan province.

Abderaz Formation is studied along Ghareh-Soo stratigraphic section, in eastern part of Kopet-dagh Sedimentary Basin which measures 958 meters in thickness. Nannofossil bioevents have been utilized to biostratigraphically classify the exposed sedimentary succession based on schemes of Sissingh (1977 modified by Perch-Nielsen, 1985), Roth (1978 modified by Bralower et al., 1995) and Burnett et al. (1998) and accordingly the rocks are attributed to Late Cenomanian to Early Campanian time interval. The results of palaeoecological studies along the succession show a decrease in high fertility marker taxa like Biscutum spp., and point to warm and oligotrophic surface water conditions in the late Cenomanian sediments i.e. upper parts of Aitamir Formation. A relative increase in high fertility taxa at the base of Abderaz Formation spanning the Cenomanian-Turonian boundary interval is also distinguishable. The Turonian part of Abderaz Formation is characterized by an increase in diversity and abundance of forms belonging to family Polycylolithaceae. Appearance of cool water taxa such as Gartnerago segmentatum, Ahmuellerella octoradiata and Kamptnerius magnificus in middle part of Abderaz Formation may probably be an indication of the Late Turonian to Campanian gradual and continuous cooling.

Pabdeh Formation has been investigated in three sections viz. the Type Section, Tang-e Hatti and the northern limb of Gurpi Anticline within the Zagros Sedimentary Basin with emphasis on calcareous nannofossils. Study of microscope slides prepared from the 1508 collected samples resulted in determination of 256 species belonging to 59 genera from 22 families of nannofossils and biostratigraphic classification was carried out based on their stratigraphic distribution. According to Martini (1971) zonal scheme, presence of NP4-NP23 nannofossil zones at the Type Section, and NP5-NP23 nannofossil zones at both Tang-e Hatti and northern limb sections have been ascertained thus indicating ‌‌Early Paleocene to Early Oligocene age for the Pabdeh Formation at these three localities. Calcareous nannofossil assemblages reveal sedimentation of Pabdeh Formation occurred in an oligotrophic, warm water environment during Paleocene-Eocene which was later on replaced by a relatively cooler water condition in Oligocene times.

Paleocene-Eocene Thermal Maximum (PETM) is a short-term climatic event that occurred about 56 million years ago, crucially affecting the global biological ecosystems, especially calcareous nannoplankton. Analysis of the fossilized remains of calcareous nannoplanktons in the sedimentary successions deposited during the said interval of time in Zagros Sedimentary Basin points to the presence of a rich nannofloral assemblage consisting of 112 species belonging to 31 genera. The observed distribution and calculated abundances of calcareous nannofossils confirm occurrence of PETM event in the area under investigation. The findings which point towards sudden release of carbon to the ocean-atmosphere system, indicate a decrease in pH of oceanic waters leading to shallowing of Carbonate Compensation Depth (CCD) and dissolution of limestones. This is reflected in the diversity and abundance of nannofloral assemblages due to the availability of carbon dioxide and increased rate of calcification process. The phenomenon also brought about a reduction in the oxygen content of atmosphere and global warming. Slower rate of carbon release during PETM as compared to that of present day, points to the possibility of a more catastrophic acidification of today’s oceans. Moreover,expected release of about 2000 pg carbon during the next 200 years (based on current trends) will result in a 2000-4000 pg increase of additional carbon in the oceanic sediments which is much in excess of what happened during PETM, thus accelerating therate of current global warming.

The Lower Cretaceous sedimentary succession of western Kopet Dagh Basin (Sarcheshmeh and Sanganeh formations) was investigated. Taking into account the considerable thickness of the studied section (1668 m) and the possibility of recording all the important events, determination of calcareous nannofossil biostratigraphy was put on the agenda. This resulted in recognition of NC5, NC6 and NC7A nannofossil zones. Accordingly the age of the Sarcheshmeh Formation within the studied section is determined as Late Barremian- Early Aptian while the age of the Sanganeh Formation is late Early Aptian- early Late Aptian. The calcareous nannofossil assemblage of Sarcheshmeh and Sanganeh Formations has a Tethyan affinity with abundant warm-water varieties such as Rhagodiscus spp. and Nannoconus spp. while the cold-water species like Repagulum parvidentatum and Seribiscutum spp. are rare.

Taking into account the extent of upper cretaceous deposits of Alborz region, determination of stage boundaries within the successions at different parts of the basin by the use of calcareous nannoflora was put on the agenda. Two stratigraphic sections viz. Alamde galandrud and Pol e zoghal were sampled at predetermined intervals. back to the laboratory, the samples were prepared using gravity settling technique and the resulting thin sections. The nannofloral assemblage of the upper cretaceous rocks of northern Alborz region reveal coniacianmaastrichtian age at Pol e zoghal (west) and campanian-early paleocene age at Alamde galandrud (east). moreover, the region was situated at low paleolatitudes and experienced a low marginal environment of deposition at the said time. the outcomes of nannostratigraphic investigations carried out in Pol e zoghal section along with the resalts of earlier studies in Alamde galandrud reveals that during the late cretaceous times the depositional center of the basin was lacated on the west and gradually shifted towards east. (i.e. sedimentation started earlier in the western parts and lasted longer in the eastern parts of the basin during late cretaceous times.)