فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و هفتم شماره 1 (پیاپی 82، بهار 1400)

Devonian deposits of the Bahram Formation with a thickness of 300 m were studied based on conodont fauna in Shahzadeh Mohammad section (33 km east of Zarand, 95 km north of Kerman city) in central Iran structural Zone. According to 31 identified species and subspecies and their stratigraphic development, nine conodont biozones belonging to the middle Givetian to the lower Famennian age were identified. The presence of Polygnathus ansatus  determines the ansatus Zone and Icriodus arkonensis arkonensis, determines the age of middle Givetian for the base of the Bahram Formation, which is the oldest age determined for the base of the Bahram Formation. Based on conodont distributions and conodont biofacies, polygnathid-icrodid biofacies are the most abundant biofacies in the section, indicating the middle shelf environment for the studied deposits.

Biostratigraphic studies of the Sarvak and Ilam formations in wells No. 1 and 14 of the Abteymour Oil Field led to the recognition of six species of foraminifers from the two mentioned formations for the first time. In this research, the species of Fischerina carinata and Spiroloculina cenomana in the Sarvak Formation and the species of Palaeosigmoilopsis apenninica and Sigmomassilina ottadunensis in the Sarvak and Ilam formations belonging to the suborder of MILIOLINA Delage and Herouard (1896) and the species Rotorbinella sp. nov. in the Sarvak and Ilam formation and Pararotalia boixae in the Sarvak and Ilam formations belonging to the suborder of ROTALIINA Delage and Herouard (1896) were identified and described. These species are not yet reported from the Sarvak and Ilam formations. Based on the identified fauna, the Sarvak Formation with a thickness of 812.98 and 238 meters in wells No. 1 and 14 respectively is Cenomanian–Turonian in age, and the Ilam Formation with a thickness of 151.7 and 136 meters in wells No. 1 and 14 respectively is Santonian–Campanian? in age.

In this paper, the biological evolution of the carbonate platform of the Taleh Zang Formation with Paleocene age in the Kermanshah region has been investigated in two stages (time interval) concentrating on fossil debris (such as algae, corals, and benthic foraminifera). For this purpose, two suitable stratigraphic of this formation in the south (Kaboutar Bala section) and southwest (Barikeh section) of Kermanshah were selected, sampled, and studied. For a broader view, the results of this study have been compared with other parts of Tethys basin around the world. The depositional environment of the studied deposits of the Taleh Zang Formation is a carbonate ramp and is probably a form a low gradient ramp due to underdeveloped coral constructions. The gradient of this platform increases from the northwest (Barikeh section) to the southwest (Kaboutar Bala section). Four biofacies were recognized in the studied successions, which include green algae, coral, green algae and benthic foraminifera as well as benthic foraminifera and green algal biofacies. In the lower parts of the Taleh Zang Formation, the presence of algal and coral biofacies (patch reefs) indicates the first stage of carbonate biological evolution of this formation, in that such biofacies has been identified in the Paleocene sequences of other Tethys sectors. Throughout the time and in the upper parts of the Taleh Zang Formation, corals have disappeared and the abundance of green algae is greatly reduced. By the presence of benthic foraminifera with low amounts of green algae, the second stage of the biological evolution of the carbonate platform of the Taleh Zang Formation in the Kermanshah region is formed. In the Early Eocene in Kermanshah region and in the studied successions, due to the seawater regression, the production of carbonates in the Taleh Zang Formation stopped and the detrital red sediments of the Kashkan Formation replaced the carbonates of the Taleh Zang Formation. However, the carbonate production of this formation continued in other areas of the Zagros sedimentary basin (Lorestan province) until the Middle Eocene.

Sequence stratigraphy of the Qom Formation deposits (in two stratigraphic sections) in the Sirjan–Abadeh region has been studied. This formation in the Sirjan area (Bujan section; with Rupelian–Chattian age and 156 m thickness), consists mainly of medium- to thick-bedded and massive limestones and marls. They are unconformably underlain by the polygenetic conglomerate with indeterminate age, and unconformably overlain by the quaternary alluvium. The Qom Formation outcrops in northern Abadeh (with Rupelian–Chattian age and 85 m thickness) consist mainly of massive and bedded limestones, shales, and conglomerates. They are conformably underlain by the Lower Red Formation and unconformably overlain by the quaternary alluvium. Eleven different microfacies, belonging to open marine (middle ramp), lagoon (inner ramp), beach, and braided streams were recognized. Based on the field investigations, deepening and shallowing patterns in microfacies, stacking patterns, and the distribution of foraminifers, four third-order depositional sequences in the Bujan section and five third-order depositional sequences in the Abadeh section have been identified. These depositional sequences are bounded by both type 1 and 2 sequence boundaries. Sequence boundaries are mainly characterized by the abrupt change in lithology and biotic components.

The Middle–Late Eocene carbonate deposits have developed in the Shan-Abad anticline as a thin belt among volcanic rocks. The nummulite banks are one of the most interesting deposits in this belt and composed of nummulite accumulations in the form of small, low-relief build-ups. Investigating three outcrops of these deposits were carried out at the eastern flank of Shan-Abad anticline in the present study. A high diversity of larger benthic foraminifera (LBF) and a small number of planktonic foraminifera are recognized, and the sedimentary environment is reconstructed.Based on LBF, three Tethyan foraminiferal biozones (SBZ 17–SBZ 19) spanning the Middle to Late Eocene interval are identified. The textural analysis and faunal assemblages reveal eleven microfacies types. These microfacies types (MFT) are deposited on a carbonate ramp model from tidal to open marine settings. Analysis of the Bartonian–Priabonian deposits based on facies distribution and paleoecology of the biotic components suggest deposition in the inner, middle and proximal outer ramp settings. The inner ramp includes proximal and distal parts. The proximal part of inner ramp is characterized by tidal flat, lagoon, and shoal belts. The distal part of inner ramp includes the nummulite banks. The open marine microfacies were deposited in mid to proximal outer ramp settings.

Ammonite biostratigraphy could be used in age determination and correlation of rock units in different sedimentary basins. Qumenjan section with 125 meters thickness is mainly formed by grey sandy limestone with grey and thick-bedded limestone intercalations. The study area is located in the eastern margin of the Lut Block. For a stratigraphical study of Lower–Upper Cretaceous deposits in southwestern of Qayen area, a stratigraphic section was selected and measured. Eight ammonites, including Anisoceras, Calycoceras, Hypoturrilites, Hysteroceras, Mantelliceras, Puzosia, and Scaphites genera and thirteen representative species were identified. Based on the identified assemblage fossils and comparison with international biozones, Hysteroceras orbignyi subzone for Late Albian age, Mantelliceras mantelli biozone for the lower part of Early Cenomanian age, Mantelliceras dixoni biozone for the upper part of Early Cenomanian age, and Turrilites costatus biozone for Middle Cenomanian age is suggested. According to identified genera and species a Late Albian–Middle Cenomanian age is assigned for ammonite bearing of the section. The first occurrence of Mantelliceras mantelli is taken as the base of Cenomanian. Compression of the identified ammonites with other basins shows that the east Iran basin was a part of Tethys Realm during late Albian–middle Cenomanian.