نشریه رخساره های رسوبی
سال هفتم شماره 1 (پیاپی 12، تابستان 1393)

The Asmari Formation in Tang-e Surkh section is composed of 294 meters of thin to medium bedded and thick to massive bedded limestone associated with marly limestone. The studied section is located in the northwest of Interior Fars. Based on deepening and shallowing patterns of microfacies، one HST and one third-order depositional sequence during Rupelian and two third-order depositional sequences during Chattian are recognized. Sequence boundaries are determined by bioclast imperforate foraminifera miliolid packstone، fine to medium grained hybrid sandstone، bioclast microconglomerate and calcareous conglomerate، respectively. The upper boundaries of sequences are defined as type 2، while the bounderies in sequences 3 and 4 are type I respectively.

Miocene silisiclastic sediments in Binalood zone consist of three lithofacies group including gravelly (Gmm، Gcm، Gci، Gh، Gt، Gp)، sandy (St، Sm، Sh، Sp، Ss، Sl) and muddy (Fm، Fl). Gravelly lithofacies are generally massive and mainly consist of volcanic and sedimentary lithic in different size. Sandy lithofacies are composed of litharenite and feldespathic volcanicarenite and rock fragments are almost volcanic as well as minor amounts of sedimentary and metamorphic rock fragments. Based on red color، absence of marine fossils، present of unimodal planar and trough cross bedding in a fining upward cycles، lithofacies analysis and architectural elements، these sedimentary rocks deposited in braided river and alluvial fan as well as playa. Based on geochemistry and petrographic data، parent rocks for these sediments، are probably felsic and intermediate igneous rocks with recycled orogen that originate in active continental margin.

Petrography، modal analysis of sandstones and major elements geochemistry of shales of Early Cambrian Zagun Formation in Sarbandan section، Central Alborz، are used to identify their provenance (including parent rocks، tectonic setting and paleo-weathering). Petrography of the sandstones and plotting their point counting data on Qt44، F47، L9 and Qm44، F45، Lt11 diagrams imply that they are arkose، with mainly a plutonic and high- to medium-grade metamorphic source rock in a basement uplift under a dry to sub-humid climate which were deposited in a transition from rift to passive margin tectonic setting. However، the major elements geochemical data show that these sandstones are dominantly arkose and the shales are dominantly iron-free. These results refer to erosion from a quartzose-sedimentary provenance (old quartz grains from rocks such as granite and acidic gneiss) and deposition in a passive continental margin tectonic setting with moderate chemical weathering under dry to sub-humid climatic condition. However، there is a discernible consistency among all different approaches (petrography، modal analysis and geochemistry) in Sarbandan section as well as the similar studied in Zagun Type section. Consequently، the results imply a uniform condition of the hinterland and the basin for deposition of the Zagun Formation in central Alborz during Early Cambrian.

Frasnian - Famennian boundary in the Kal-e-Sardar section (East of Tabas، Central Iran) is investigated on the basis of conodonts. Distribution of thirty-three species and subspecies in the stratigraphic column enables us to recognize a barren interval and five biozones; Upper rhenana، upper part of Upper rhenana - linguiformis، Lower to Middle triangularis، Upper triangularis، Lower crepida. Biofacies analysis shows a deepening trend through the Late Frasnian and then a sharp sea level fall present at the base of early Famennian sequences. Deeper environment governs through the Famennian stage. A new range is proposed for P. planarius; Lower hassi - linguiformis zones.

The Kopet-Dagh basin extended in the north and north east of Iran and consists of marine strata from Middle Jurassic to Paleogene time. Abtalkh Formation is one of the thickest lithostratigraphic units of Cretaceous in the Kopet-Dagh basin and is composed of light gray، green to bluish marl and silty marl. The Abtalkh Formation conformably overlies the marls and chalky limestones of the Abderaz Formation and is conformably overlain by the Nayzar Formation (sandstone، silty marl and limestone). In this study، the Padeha stratigraphical section in the eastern Kopet-Dagh basin was selected and studied in high resolution for its calcareous nannofossil biochronology. Padeha section contains very abundant، rich and moderately preserved calcareous nannofossil assemblages of Tethyan realm. A total of 268 samples in Padeha stratigraphical section were collected from the Abderaz، Abtalkh and Nayzar formations. The thickness of measured Abtalkh Formation in Padeha section was 974. 5 (m). One hundred and fourteen nannoplanktonic species belonging to forty nine genera and seventeen families were identified and the biostratigraphic study allowed the recognition of the calcareous nannofossil biozones of Sissingh (1977)، emended by Perch-Nielsen (1985) and Burnett (1998). From bottom to top، identified biozones in the Padeha section including a part of CC19، CC20، CC21، CC22، probably a part of CC23a and a part of UC14dTP، UC15bTP، UC15cTP، UC15dTP and probably a part of UC16. The results of this study indicate that the age of Abtalkh Formation in the Padeha section spans from late Early Campanian to Latest Campanian.

Planktonic foraminifera are useful in determining the relative age of the Upper Cretaceous strata. Based on distribution of planktonic foraminifera in Kuh-e Siah section (212 m thickness)، eight biozones have been recognized including Dicarinella concavata Interval Zone (Earliest Santonian)، Dicarinella asymetrica Total Range Zone (Santonian to Earliest Campanian)، Globotruncanita elevata Partial Range Zone (Early Campanian)، Globotruncana ventricosa Interval Zone (Middle to Late Campanian)، Radotruncana calcarata Total Range Zone (Late Campanian)، Globotruncanella havanensis Partial Range Zone (Late Campanian)، Globotruncana aegyptiaca Interval Zone (Late to Latest Campanian) and Gansserina gansseri Interval Zone (Latest Campanian to Early Maastrichtian). The study of the Gurpi Formation at Kuh-e Siah anticline and its comparison with the Tang-e Bulfares (Early Santonian to Middle Maastrichtion) and Aghar anticline (Late Santonian to Middle Maastrichtioan) sections، show that the sedimentation of the Gurpi Formation has been started in Dehdasht area (Kuh-eSiah section) at the Earliest Santonian time، while in the Bulfares and Aghar sections، sedimentation started at the Early Santonian and Late Santonian time respectively. Three morph type groups of planktonic foraminifera were recognized during the Santonian to Maastrichtian at the Kuh-e Siah anticline. The results of this study were similar with depth fluctuations of sedimentary basin in Bulfares and Aghar sections that can be affected by global changes in sea level.

The Asmari Formation is a thick carbonate sequence in Zagros foreland basin. It was deposited during Oligocene – Early Miocene ages. In order to interpret the depositional environment and sequence stratigraphy، Firuzabad section were compared with 4 sections of Asmari Formation in the Zagros basin. Four different sub environments were identified in the Asmari Formation based on microfacies analysis including tidal flat، lagoon، shoal، open marine. These depositional environments correspond to inner، middle and outer ramp. Two third-order sequences have been recognized in the Firuzabad section، on the basis of deepening and shallowing patterns in the microfacies and the distribution of the Oligocene foraminifers. These sequences were correlated with the identified sequences of Dehluran، Mamulan، Dill and Tange-Ab Jahrum sections.

In this study، depositional environment and provenance of sandstones of the Surijeh Formation (Lower Cretaceous) in the Abgarm section in the Kopet-Dagh basin are investigated. Analysis of Sedimentary facies in this section shows that there are two clastic (continental and coastal plain) and two carbonate (coastal plain) facies associations are present. The results of modal analysis and geochemical data show that siliciclastic sediments are derived from recycled orogenic and quartzose sedimentary source rock (recycled orogen). The use of discriminant function diagrams shows these sandstones plotted in the passive continental margin. Chemical index of alteration (CIA) for these rocks suggests a moderately high chemical weathering of the source terrains. The geochemical results are very similar to petrographicl data that show semi-humid to semi-arid climate conditions.