JOURNAL OF STRATIGRAPHY AND SEDIMENTOLOGY RESEARCHES
Year:2012 | Volume:28 | Issue:2 (47)|Papers Count:6

Aitamir Formation (Albian-Cenomanian) in the Kopet-Dagh Basin has diverse trace fossils and several shell beds. These trace fossils contain diverse ethological patterns, including domichnia, fodinichnia, grazing, equilibrichnia, navichnia, chemichnia and fugichnia. The types of shell beds distinguished based on differences in sedimentological, palaeoecological and taphonomic features. Shell beds and sandstone layers containing characteristic trace fossils represent a storm-influenced succession. Bioturbation increases markedly towards the top of the shell beds as the energy of deposition declines to allow colonization by benthonic faunal assemblages. Types of shell beds generally including (1) initial firmground substrates in foreshore to offshore environments as indicated by the Glossifungites ichnofacies, includingGastrochaenolites, Rhizocorallium and Thalassinoides, (2) basal storm-erosive lag deposits, (3) re-worked shell beds of main storm deposits as indicated by the Glossifungites ichnofacies, including Ophiomorpha (4) fair-weather shell beds in a near-shore position and above fair-weather wave base. (5) Composite or multiple-event concentration from time averaged and multiple event deposit. Seven trace fossil assemblages are identified in Aitamir Formation deposits. They are (1) the Zoophycos Ichnofacies (2) the distal Cruziana ichnofacies, (3) the archetypical Cruziana ichnofacies, (4) the mixed Skolithos-Cruziana ichnofacies, (5) the distal Skolithos ichnofacies, (6) the archetypal Skolithos Ichnofacies, and (7) impoverished expression of the Skolithos ichnofacies. This succession of shell beds and trace fossil assemblages reflects a gradational decrease in hydraulic energy levels induced by storms.

Sarvak Formation (late Albian-middle Turonian) is one of the important reservoir units after Asmari (Oligo-Miocene) in southwest Iran that host an important hydrocarbon reserves in this region. Due to facies and environmental variations as well as complex diagenetic history, its reservoir properties show intense complexity and heterogeneity. To understanding these imposed heterogeneities a comprehensive reservoir study including facies analysis, diagenetic study and sequence stratigraphy are carried out. According to facies analysis study, carbonates of this formation deposited in a homoclinal ramp-type platform. Low diversity of determined microfacies as well as other properties, such as dominance of mud-dominated facies in this field, all is indication of a leeward ramp. Main diagenetic processes effected carbonates of this unit are extensive dissolution (in two step: eogenetic and telogenetic), dolomitization (in two ways: mixing zone and stylolite related), cementation (include meteoric, shallow and deep burial cements), micritization, mechanical and chemical compaction (stylolitization), dedolomitization, silicification, pyritization, recrystallization and fracturing. Paragenetic sequence of diagenetic events of this formation above Cenomanian-Turonian boundary and below it showed two different histories for these two parts. Three 3rd order are recognized in sequence stratigraphic studies in part of Sarvak Formation belong to middle Cenomanian to middle Turonian time span. Examining facies distribution patterns and diagenetic events in a sequence stratigraphic framework indicate close relationships and predictability of diagenetic alterations.

The present study is an evaluation of diagenetic processes and reservoir quality of upper Khami Group in Bibi Hakimeh oil field. The Khami Group is divided into Upper (Fahliyan, Gadvan and Dariyan formations) and lower parts (Surmeh and Haith formations). Lithologically, Fahliyan and Dariyan formations and Khalij Member of the Gadvan Formation are carbonate and Gadvan Formation is shale. The determined diagenetic processes are dolomitization, glauconitization, anhydritization, mechanical compaction and stylolitization, chertification, pyritization in the upper Khami. Reservoir geological model for describing the structure and fault effects, iso-grade mud loss and fracture maps were constructed by reservoir management system (RMS) software. The results revealed that fractures development and as well as the effect of diagenetic processes such as dolomitization and dissolution seem to have increased the reservoir quality. There is good development of fractures in this reservoir. In general, existence of fractures and effects of processes such as dolomitization and dissolution seem to increase the reservoir quality in this field.

In order to biostratigraphy of the Garau Formation in the centeral Lurestan one subsurface section (Naft well) in Naft anticline, south Kermanshah was selected and studied. The drilled thickness of the Garau Formation in this section is up to 485 meters and lithologically composed of argillaceous limestones and dark gray marls. In this research 1150 thin sections of subsurface Naft well section were studied. In biostratigraphic studies of the Garau Formation in study section 61 species belong to 17 genera of planktonic foraminifera were recognized and 9 biozones were identified. Based on distribution of fossils and biozones identificated, the age of the Garau Formation in drilled part of the subsurface Naft well section is Early Aptian to Early Cenomanian.

Calcareous nannofossils and Ammonites have been studied in the Sarcheshmeh and Sanganeh Formations at the Takal Kuh section in the western part of the Kopet-Dagh Basin. In the studied section ammonite biozones that are present in Sarcheshmeh Formation are Heteroceras spp. Zone, Martelite securiformis Zone, Deshayesites oglanlensis Zone, Deshayesites weissi Zone and the lower part of Deshayesite deshayesi Zone and the biozones which are recognized in Sanganeh Formation are the Upper part Deshayesite deshayesi Zone and Dufrenyia sp. Zone. According to the ammonite fauna present the age of the Sacheshmeh Formation is determined to be Late Barremian-Early Aptian and that of Sanganeh Formation to be Early Aptian. In this section the calcareous nannofossil zones Watznaueria oblonga Zone (NC5) and Chiastozygus litterarius Zone (NC6) are located within Sarcheshmeh Formation and the Upper part of Chiastozygus litterarius Zone (NC6) and the Rhagodiscus angustus Zone (NC7A) are found in the Sanganeh Formation. On the basis of calcareous nannofossil data the age of the Sarchechmeh Formation is found to be Late Barremian-Early Aptian while that of the Sanganeh Formation is estimated to be Early Aptian-early Late Aptian. Calcareous nannofossils data recorded the presence of Oceanic Anoxic Event 1a (OAE 1a) at the upper part of NC6 and the lower part of NC7A Zone (lowermost 50 meters of Sanganeh Formation meters). Ammonites are not present at the Oceanic anoxic event OAE 1a interval, but but appear at Sarcheshmeh-Sanganeh boundary, and are used for dating the event. Based on the presence of Deshayesites cf. involutus, Deshayesites cf. consobrinoides and Deshayesites deshayesi at the first part of the interval Deshayesites deshayesi ammonite biozone has been determined and accordingly the OAE 1a event is recorded within the Deshayesites deshayesi Zone of the studied section.

The Sarvak Formation in Tang -e-Chenarbashi with 712 meters thickness encompasses Albian- Cenomanian planktonic foraminifera. In the studied section, surveying the Albian- Cenomanian boundary is indicated that Rotalipora appeninica Zone not be recognized. Paracostellagerina libyca can be to consider as a marker for Albian-Cenomanian boundary, absence of the Albian marker foraminifera permit us to consider the first occurrence of this species as the bigining of Cenomanian. Also Favosella voloshinae, Paracostellagerina libyca are report for first time from Iran.