فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال بیست و هفتم شماره 3 (پیاپی 44، پاییز 1390)

The Kangan (Early Triasic) and Upper Dalan (Late Permian) formations form the important gas reservoirs in Iran. The ooidal grainstone and mudstone facies form more than of 75 percent of Kangan Formation. Therefore, recognition of controlling processes of reservoir properties on these facies lead to understand the reservoir quality on whole formation. In this study, based on recognition of microfacies and depositional environments, petrophysical properties of Kangan Formation are investigated. Results show that the grain-dominated facies have better reservoir quality, and dissolution of allochems on these facies (grain dominated), dolomitization and fracturing caused to increasing reservoir properties. However, calcite cementation, anhydritization and compaction decreased the reservoir quality.

Lithofacies analysis and interpretation of architectural elements of Oligocene silisiclastic deposits in Binaload Zone were investigated in Baghshan-Gach area, north of Neyshabour. This study led to identification of 14 lithofacies and 4 architectural elements in the sequence of 150 meter thick. Lithofacies are classified into three categories including coarse grain (Gmg, Gcm, Gmm, Gh, Gp and Gt), medium grain (Sh,Sp,St,Sr,Sm and Sl), and fine grain (Fl,Fm). The architectural elements are CH, SB, LV and SG. It is interpreted that Oligocene silisiclasic sediments have been deposited in braided river system, based on lithofacies analysis and architectural elements. Petrofacies analysis indicates that these rocks had oroigin from the magmatic arc and deposited under arid climatic condition. paleocurrent analysis represents that the river was flowing from NE to SW direction.

The Ilam Formation (Santonian to Campanian), as an oil reservoir rock in a Zagros field, composed of carbonate facies. In this study, two surface sections (Payun and Kabir Kuh anticline) and one subsurface section (DA#a), 6 microfacies have been recognized. These facies deposited in lagoon to deep marine environment. In this formation, 446 thin sections were studied petrographically and 93 powered samples geochemically analysed.Based on major and minor elements and oxygen and carbon isotope values in the Ilam Formation samples and their comparison with the results obtained from mixed aragonite and calcite fields published by different researchers, original carbonate mineralogy of the Ilam Formation was mixed aragonite and calcite. Oxygen and carbone isotopes indicate that these carbonates are mainly influenced by meteoric diagenesis. Paleotemperature calculation based on heaviest oxygen isotope value) -3.60 ‰ PDB), indicate that ambient water temperature during precipitations of the Ilam carbonates was 28°C. Major, minor and isotopic data in carbonates are depend on their mineralogy and mineralogy itself changes during diagenetic processes. By petrographic studies alone, cannot understand the original mineralogy and kind of diagenetic processes on carbonates, therefore must be use elemental and isotopic data as complementary studies. Different carbonate minerals are formed in different temperature, salinity and Ca/Mg ratio. In addition, major elements (Ca, Mg), minor elements (Sr, Na, Fe, Mn) and oxygen and carbon isotopes are also change.

Padeha and Bahram formations of Shahzadeh Mohammad area are 597m in thickness that contain well – preserved and abundant palynomorphs consisting of acritarchs, miospores, chitinozoans and scolecodonts. In this paper, acritarchs taxa are presented only. These include: Chomotriletes vedugensis, Gorgonisphaeridium abstrusum, Gorgonisphaeridium comdensum Gorgonisphaeridium sp., Lophosphaeridium deminutum, Maranhites perplexus, Papulogobata annulata, Naivifusa exilis, Stellinium micropolygonale, Stellium comptum, Deltotosoma intonsum, Dictyotidium prolatum, Helosphaeridium microclavatum, Somphophragma miscellum, Tornacia sarjeantii and Veryhachum downiei,. These marine palynomorph taxa suggest a Late Devonian for these two rock units in the Kerman province. These acritarch taxa are comparable to those have reported from the Late Devonian (Frasnian - Famenian) of other parts of Iran (Alborz, Zagros and Central Iranian basins) and elsewhere (Saudi Arabia, southern Europe, Australia and North Africa). On the other hand, based on parasinophyte taxa a shallow marine environment is suggested for depositional environment of the Upper Devonian strata in the Shahzadeh Mohammad area, northern Kerman province.

The Cretaceous limestone and Jurassic shale are the main country rocks of Zn-Pb Irankuh mine. Jurassic units in this region are composed of dark and olive shale and sandstone that are unconformably covered by Cretaceous carbonate rocks. Mineralization has mainly occurred in carbonate rocks, but because of the high concentration of heavy metals in shales, they are selected for the investigation of their role as a probable source of metals in mineralization. For this purpose, field, geochemical and mineralogical studies were carried on the samples selected from shale unit. Also, due to the importance of the fluid inclusions in study of the origin of deposits, some samples were selected and prepared for this purpose.Atomic absorption geochemical analysis results for Zn, Pb, Ag, Ni elements has revealed a wide range of changes in their concentration in faulted rocks, unaffected rocks from the ore bearing fluids and mineralized regions. Microthermometric studies of the samples show a homogenization temperature range of 100-160C and a salinity range of 17-22 eq. wt% NaCl which is well confined to that range of Mississippi valley-type Pb-Zn ore deposits. Based on the results of this research, it seems that ore bearing fluids in this area have many similarities with the basinal brines and it seems that ore elements were leached from the shale units and upwelled along the fault and fractures which has at last mixed with ground waters and mineralization has occurred in the carbonate rocks.

The Chamanbid Formation at the type section has been measured for palynostratigraphical studies, however, the upper part of section (with a thickness of 240 m) was palynologically productive. Diverse and well- preserved palynofloras occur in the upper part of the type section. Microflora (trilete and monolete spores and pollen) together with dinoflagellate cyst, scolecodont, foraminiferal test linings, fungal and algal spores are present. Thirty nine species of spores (28 genera) and 13 species of pollen (11 genera) are identified. Representatives of Corollina, Klukisporites and Cicatricosisporites are particularly abundant.Based on stratigraphic distribution of miospores, three distinctive stratigraphically successive palynofloras informally termed in ascending order Assemblages zone A, B and C are identified within the upper part of Chamanbid Formation. The oldest of the three assemblages, Assemblage zone A is characterized by the appearance of miospore species Ruffordiaspora australiensis. The Assemblage zone B is defined by the co-occurrence of the Laevigatosporites ovatus and Trilobosporites trioreticulatus. The Assemblage zone C is marked by the appearance of Plicatella sp. Based on the co-occurrence of certain miospore species, Ruffordiaspora australiensis (Tithonian-Campanian) and Ruffordiaspora ludbrookiae (Tithonian-Albian) the upper part of Chamanbid palynofloras are collectively dated as Upper Jurassic (Tithonian), thus corroborating the ammonoid evidence.

Qeshm is the largest island in the Persian Gulf. It is expanded along the coast and located at the furthest southeast of Zagros sedimentary-structural unit under the Bandar Abbas flat and it is a part of it. The stratigraphic units in this island are Hormoz Series, Mishan Formation, Aghajari Formation and Quaternary deposits. The calcareous marine terraces of this island are the important part of deposits assign to the Quaternary period. These deposits indicate the relative variance of sea level in Pleistocene and Holocene. Petrogarphical studies on the 40 samples collected from the terraces led to identification of 10 microfacies including mudstone, benthic foraminifera wackestone, oyster packstone, bioclastic mudstone, bioclastic wackestone, bioclastic packstone, bioclastic packstone- grainstone, oolitic packstone, intraclastic packstone and sandy bioclastic packstone. The facies show characteristics of 5 various depositional conditions including: supratidal, intertidal, lagoon, barriers and abundant tidal channel. Based on sediment analysis the environmental condition of inner ramp is indicated by the quantity of tidal channels of these sediments. Sediments are consist of these minerals: carbonates, quartz, clay, plagioclase, halite and clay minerals (chlorite and illite). These minerals show the entrance of the deposits from land by fluvial flows and distribution by marine flows. Geochemical studies of calcareous marine terraces indicate low salinity levels, the semi- reducing to reducing conditions the growth of the forming the terrace and primary composition of the deposits of bio calcite of magnesium.

As ostracods are excellent index in determining the paleoenvironment, age and paleoecology of sediments, the ostracods in marls units 1 and 3 of Tarbur Formation have been studied. Tarbur Formation with 712 m thickness is divided into 6 units. In this study, 60 samples of marls units 1 and 3 have been washed, and studied and totally 21 species identified. The ostracods indicate a Maestrichtian age and warm, oxygen-rich and shallow depositional environment for the studied units.