SEDIMENTARY FACIES
Year:2011 | Volume:3 | Issue:2|Papers Count:8

The Asmari Formation (Oligo-Miocene) consists of carbonate and terrigenous deposits (Ahwaz Member) in the Aghajari Oil Field. In the Aghajari Well No.61, the Ahwaz Sandstone Member is unconformably bounded by underlain Pabdeh Formation and the overlying upper Asmari Member. Petrograpgic studies of the terrigenous deposits of the Ahwaz Member led to recognition of open marine, incised valley, barrier, lagoon, tidal flat, elongate and lobate deltas and fluvial facies deposits. These facies were formed after Late Ruplian tectonic activity. Based on this study, the lower unit of the Ahwaz Sandstone Member was formed in a mixed carbonate-terrigenous distally steepened ramp, but its upper unit, on the other hand, was formed on a homoclinal ramp. Facies variations within the Ahwas Member can be related to tectonic activity, sea level fluctuations and depositional processes.

The Gurpi Formation in Mish-Khas Section, north of Ilam, consists of 310m marl with intercalations of limy marl with two formal members of Seymareh and Emam-Hasan. The Seymareh Member is composed of limestone and Emam-Hasan Member is argillaceous limestone. This rock unit was deposited from Late Santonian through Late Paleocene based on identified planktonic foraminifera. At this locality, ten species of echinoids from Seymareh Member identified and the age based on echinoids is Upper Campanian -Lower Maastrichtian. The echinoids are: Goniopygus superbus, Hemiaster noemae, Orthopsis miliaris, Salenia nutrix, Hemipneustes compressus, Coptodiscus noemiae, Pygurostoma morgani, Conulus douvillei, Micraster sp., and Coenholectypus inflates. At this locality, Paleobiogeography is determined based on two factors planktonic foraminifera and echinoids. Comparing planktonic foraminifera and echinoids assemblages recovered from this section with those of Cretaceous biogeographical provinces indicate a close similarity with those of low latitudinal at northern hemisphere and Tethyan realm.

In this research, biostratigraphy of the Qom Formation in Chenar area (northwest of Kashan) was studies. The thickness of the formation at this section is about 147m. It consists mainly of marly limestone and medium to massive bedded limestone. At this section, the Qom Formation nonconformably lies between Eocene Volcanic at the base, and recent alluvium at the top.112 samples collected and studied from this section led to identification of 28 genera and 38 species of benthic foraminifera. Since there is no formal biozonation for the Qom Formation and similarity of assemblage with the assemblage that was recorded from Asmari Formation by wynd (1965) and Laursen and et al. (2009), the published assemblage for the Asmari Formation used here. Based on the recognized foraminifera, the assemblage is comparable to: Lepidocyclina-Operculina- Ditrupa- Assemblage Zone. Based on identified foraminifera, the age of the Qom Formation in the studied section is Oligocene (Rupelian- Chattian). The sedimentation trend for the studied section is parallel to main sedimentation trend of the Qom Formation in central Iran.Sedimentation of the Qom Formation continued to Aqutanian toward southeast.

In order to study the genus and species of ostracods of the Oligo-Miocene and their paleoecological significant in Kerman Province, one section (Gefriz) has been measured and sampled. The Gefriz section is located about 50 km north of Baft and south west of Kerman. Gefriz section contains microfauna of foraminifera and ostracods. The studied section disconformably overlies the Eocene Volcano sedimentary rocks, while at the top an erosional surface occurs.The study of ostracods led also to reorganization of 19 genera and 21 species.The ostracods belong to podocopids and platycopids orders are present.Constituents of this assemblage of ostracods community confirm a favorable condition during the deposition of the strata, specially well- oxygen, light, food and show a warm environment. These ostracods and associated foraminifers are representing an Early Miocene (Aquitanian) age for this succession.

In order to study Early Cretaceous rudists in east of Iran, a section in southwest of Qayen has been selected and measured. The thickness of section is about 81 meters. The sequence is composed of: conglomerate, sandstone and massive limestones with rich fauna of rudists, gastropods and foraminifera (orbitolinid). Based on systematic investigations, two genera and four species of rudists consist of Pseudotoucasia catalaunica, Pseudotoucasia santanderensis, Pseudotoucasia sp. and Toucasia carinata have been identified. Late Aptian age is suggested for studied section with respect to the identified taxa of rudists, orbitolina species, and stratigraphic position. The recognized rudists show resemblances to those are reported from Tethian realm, especially from northern margin of Tethys. This similarity confirms fauna relationship among these areas.

Middle and Late Jurassic strata have a great thickness in the Binalud Mountain Range Zone (northeast Iran). These strata consist mainly of shale, marl, limestone and marly limestone with abundant ammonite fauna. Phylloceratidae have the highest percentage (~40%) among the fauna and are the aim of the present study. The following taxa are identified: Phylloceras sp., Phylloceras aff. kudernatschi, Phylloceras velaini, Holcophylloceras zignodianum, Callipylloceras disputabile, Calliphylloceras demidoffi, Ptychophylloceras (Tatrophylloceras) biarcuatum, Ptychophylloceras (Tatrophylloceras) euphyllum, Holcolissoceras sp., Sowerbyceras sp., Sowerbyceras tortisulcatum.

This research is focused on isotopic analysis data of Sarcheshmeh and Sanganeh Formations in Takal Kuh area in west Kopet Dagh basin. Based on stratigraphic and paleontological studies of ammonites, Late Barremian- Early Aptian age for Sarcheshmeh and Early Aptian age for Sanganeh formations were suggested in study area. Carbon and oxygen isotopes values were analyzed for 35 samples. Variation of carbon isotopes in studied sections were correlated with biostratigraphic data and compared with isotopic data of Aptian type section in Europe and some other sections in Tethys. This correlation shows well similarities. Moreover, based on isotopic and paleontologic data, basal shale of the Sanganeh Formation is interpreted as OAE1a (Oceanic Anoxic Event) which is correlated with Deshayesites deshayesi biozone. Calculated temperature of ambient water during deposition of Barremian-Aptian deposits is supported by paleogeographic maps of Kopet-Dagh.

Sarcheshmeh Formation (Aptian) exposed in the Khur syncline with northwest- southeast trend, (eastern Kopet-Dagh zone). It consists mainly of shale, calcareous shale and thin bedded limestone with trace fossils. Sarcheshmeh Formation overly conformable on Tirgan Formation and its upper boundary is eroded at this section. Five ichnogenera; Paleodictyon, Zoophycos, Scolicia, Arthrophycus, Chondrites, and three ichnospecies; P aleodictyon maximum, Paleodictyon strozzi, Paleodictyon miocenicum, were identified. Sarcheshmeh Formation has been interpreted as a shallow marine deposit; it may be, however deposited in the deeper environment such as, outer ramp with lower oxygen level, where these ichnofossils formed.