نشریه رخساره های رسوبی
سال پنجم شماره 1 (پیاپی 8، تابستان 1391)

In This study، large benthic foraminifera of Qom Formation in Chenar area (northwestern Kashan) with 147 m thickness are investigated. 112 thin sections were prepared and distribution of benthic foraminifera was analyzed to reconstruct paleoenvironmental condition. Sea level fluctuations could be observed from bottom to top in the studied section. Based on large benthic foraminifera assemblages and microfacies features، three major depositional environments (inner shelf، middle shelf & outer shelf) were defined. The inner shelf facies is characterized by wackstone-packstone، dominated by miliolid and small perforate foraminifera. The middle shelf facies is represented by packstone-grainstone with diverse assemblage of large perforate benthic foraminifera. Outer shelf facies is dominated by large perforate benthic foraminifera as well as planktonic foraminifera. The distribution of the Oligocene large benthic foraminifera in the studied area indicates that shallow marine carbonate sediments of the Qom Formation were deposited in a photic zone of tropical to sub-tropical environments.

The Eshghabad-Sule drainage basin with about 81. 365 Km2 is located in southwest of Quchan. The Eshghabad-Sule River is a gravel bar-bed river which its grain size decreased exponentially downstream. This may be related to selective transport of clasts on the streambed and abrasion during transport. To understand the grain size variations and effective factors in downstream fining، 34 samples have been analyzed. As results، 3 discontinuities and 4 sedimentary links were identified. In this basin، the role of hydraulic sorting in comparative with abrasion is more effective in downstream fining of grain size in each sedimentary link. Calculation of grain size parameters show that in this type of river، sediments are mostly poorly to very poorly sorted، positive skewed and platykurtic to leptokurtic. The identified lithofacies in this river are consist of matrix supported gravel (Gmm)، grain supported gravel (Gcm)، grain supported gravel with horizontal bedding (Gh)، sand with horizontal bedding (Sh)، laminated mud (Fl) and massive mud (Fm). Existing facies have formed in 4 architectural elements such as Channel (CH)، Gravity flow deposits (SG)، Gravel bars and Bed forms (GB) and Fine grain classtic deposits (FF). Based on identified facies associations and architectural elements، the sedimentary model of Eshghabad–Sule is gravelly braided river system.

In this study، Neogene deposits of eastern Kopet-Dagh and east central Iran have been investigated. These deposits in the eastern Kopet-Dagh Basin consist of two lithofacies associations including gravelly (Gcm، Gmm، Gmg، Gh) and sandy (Sm) that form within four structural elements (SG، GB، SB، CH). From base to up، they were deposited in the braided river with sandy bed load in the alluvial fan depositional systems near the source area. Sequence stratigraphic analysis of Neogene deposits، based on lithofacies variations، indicated that these sediments formed in an area with the low accommodation space. Petrography study indicates that they were derived from collision and recycled orogen tectonic setting. Neogene deposits in the studied area in the east Central Iran are composed of four lithofacies associations including gravelly (Gcm، Gmm، Gmg، Gh، Gt، Gp)، sandy (Sm، Sh، St، Sp)، fine grain (siltstone) (Fm) and evaprite (P) that formed within five structural elements including SG، GB، SB، CH، FF. These sediments، from base to up، were deposited in playa and proximal to mid sandy-gravelly bed braided river in alluvial fan depositional systems. Sequence stratigraphic analysis indicates that these deposits consist of two sedimentary sequences. The first sequence belongs to high accommodation space and the second one formed during the low accommodation space. Sandstones and conglomerates composition as well as tectonic position of area indicate that the tectonic settings of the source area was probably arc orogen and continental block.

Both trace fossils and lithofacies of Binalood’s Oligocene deposits have been studied in Damanjan and Taghan sections، north Neyshabouer. Identified trace fossils include Arenicolites isp.، Cochlichnus isp.، Scoyenia isp.، Steinichnus isp.، Taenidium barretti، Horizontal U-shaped burrows، J–shaped burrows and Root trace. These trace fossils belong to Scoyenia ichnofacies، which can be found in sandstone layers. The studies of these trace fossils show that Oligocene deposit has been deposited in fluvial depositional system.

Electrofacies is a deterministic or analytical way to perform well logs data partitioning، which shows variation of geologic or reservoir characteristics. In this paper، we used well logs of two cored wells at one of the oil fields in south of Iran. An initial electrofacies model was developed based on well logs which included of 25 facies. Corresponds facies in this model merged together according to core micro facies analysis that showed 5 sedimentary facies associations. So it optimized by transmuting to new model (5 facies). Results of optimized model showed good conformity with core micro facies (in cored wells). Finally، we propagated it to all wells and simulated sediment facies in all wells of the subjected oil field.

In this study، Gurpi Formation at Mook section has been sampled and studied. Taxonomical studies of calcareous nannofossils lead to identification of 23 genera and 44 species at the Mook section. According to the first occurrence of index species and fossil assemblages، seven calcareous nannofossil biozones (CC21- CC26 of Sissingh، 1997) and biozone NP1 of Martini (1971) equivalent to biozone CP1a of Okada and Bukry (1980) at the Mook section have been recognized. Based on these biozones، age of the Gurpi Formation in SE of Shiraz، is Late Campanian to Early Danian. On the bases of paleoecological interpretation، Gurpi Formation at the Mook section was deposited in low latitude and deep marine environment. But، the depth of the basin decreases toward the top of the Gurpi Formation at this section.

Sarvak Formation of Bangestan Group (Cenomanian-Turonian) is a carbonate sequence of Cretaceous system in the Zagros Basin. In this research، an outcrop of this formation in Tang-e-Bulfares، about 60 Km east of Ramhormoz (Khuzestan Province) and in southern part of Bangestan anticline، has been studied. Diagenetic processes that have affected Sarvak Formation were evaluated using polarizing and cathodoluminescence microscopes and the paragenetic sequence of were interpreted. The most important diagenetic processes which have involved limestones of upper part of Sarvak Formation include: micritization، neomorphism، cementation، mechanical compaction، chemical compaction، dissolution، fracturing and development of calcitic veins. In general، processes such as dissolution، fracturing and in specific conditions stylolitization have increased reservoir quality in the studied section and the processes of micritization، cementation، compaction and development of calcitic veins have decreased the potential of this formation as a suitable petroleum reservoir. The results of this research reveal that destructive processes have had more influence and so the reservoir quality of the upper part of Sarvak Formation has been reduced by diagenesis. Also، study of major and minor elements reveals a closed to semi-closed diagenetic system and probably the high Mg-calcite was a primary mineralogy for carbonate rocks of the studied formation. Based on the Sr/Na versus Mg graph، palaeoclimatic conditions during deposition of the Sarvak Formation may have been similar to the present-time temperate regions.