RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2006 | Volume:23 | Issue:1|Papers Count:18

Brachiopoda fauna of Badamu Formation in the Hojedk section (north of Kerman) is studied recognizing 9 genera and 13 species as follows:Holcorhynchia standishensis, Conarosia rotundata, Conarosia sp., Baeorhynchia elegantula, Baeorhynchia nitida, Baeorhynchia transversa, Rhynchonelloidea ruthenensis, Cymatorhynchia singularis, Sphaeroidothyris arabica, Sphaeroidothyris sphaeroidalis, Orthotoma sp., Arabicella ovalis, Plectothyris sp., and Sphaeroidothyris arabica, Arabicella ovalis, Ptyctothyris sp., and Orthotoma sp.Based on the stratigraphical value these Brachiopoda can be classified into two biozones. The age of the first biozone based on the stratigraphical value of species Holcorhynchia standishensis is Toarcian and equals variabilis, thouasense and levesquei ammonite zones. The age of the second biozone based on the stratigraphical value of their Brachiopoda is Early-Middle Bajocian, which corresponeds to opalium- humphriesianum ammonite zones.Also, the frquencies above mentioned of Brachiopoda were calculated which was recognized Rhynchonellid order constitutes about eighty percent of them. Moreover, the distribution of Brachiopoda was studied in various regions of the world.

In this research, Marbor river catchment (hydrologic unit of Kahredan) with 800 square kilometers area, located in south part of Esfahan province, is studied. Landslide distribution map of landslide was obtained using aerial photos, geological maps and field survey. Moreover by applying the other information sources such as maps, the factors affecting landslide (8 factors) were determined and proper maps in 1:50000 scales were prepared.In order to promote accuracy, speed and facility, descriptive and spatial data were digitized using Ilwis software. A number of 4 conventional methods in Marbor catchment were analyzed.Before analyzing the methods, using effective parameters in each method, the landslide hazard map with appropriate classes was prepared. Using landslide Index equation and landslide precision, different methods were analyzed and compared. Through the obtained index and comparing landslide distribution map with landslide hazard zonation map results (obtained with each method) the best methods were as fallows: bivariate method of Information Value, bivariate method of density area, multivariate using linear regression analysis and multivariate using discriminant analysis, respectively. Finally, bivariate method, despite its simplicity, has appropriate accuracy, so that the ultimate map is better overlapped to landslide potential of the region.

Eocene volcanic rocks present very good exposure in south-west of Zafarghand (SE of Ardestan, Isfahan province). One phase of this volcanic succession has shoshonitic affinity.Thomsonite, Calcite, Datolite, Celadonite, Muscovite, Mesolite, and Clinozoisite have formed in cavities, joints and cracks of shoshonites. These minerals are the result of very low grade metamorphism or hydrothennal alteration of shoshonites. Chemistry of these minerals shows that the mineral bearing fluids has enriched in Ca, AI, Si, B, Na, K, OH, CO2,and H2O.

A complete succesion of the Late Ghzelian-Asselian rocks crops out at the Zaladu section in Ozbak-kuh area. Three members have been identified in this section. Member 1 consists of conglomerate, sandstone, as well as green and red shales interbedded with sandy limestone.Member 2 is limestone. Member 3 consists of thick to massive dolomite. Index fusulinids of the Late Ghezelian including, Rauserites, Rushenzevites, Schellwienia and Asselian genera like Pseudoschwagerina, Rugosofusulina have been recognized in member 2. Therefore, on the basis of these findings the Carboniferous-Permian boundary is considered to be continious in this area. This complete succesion of the Late Ghezelian-Asselian rocks is introduced for the first time in Iran. The succesion is similar to the other areas in southern Tethyan basin.

The studies of microfauna of Late Permian deposits in Chahriseh area, NE Isfahan, Central Iran, revealed that fossiliferous Late Permian sediments unconformably overlays Late Devonian strata (Late Famennian).Based on conodont and palynomorph studies, a hiatus can be considered in this area comprising the whole Carboniferous and Early Permian. This hiatus can be attributed to Hercynian uplifting and erosion by see-level fall caused by Permo-Carboniferous ice sheets and removal of enormous thickness of sediments.Late Permian gray thin to thick bedded limestones contain abundant smaller foraminifers, algae, corals, sponges, gastropods, bivalves, brachiopods, bryozoans, trilobites, etc., and ends with a. lateritic red bed. Middle Triassic sandstones and then yellowish brown thick bedded dolomites are overlain the Permian sediments. The laterite horizon and hiatus here may be related to the uplifting and epirogenic phase caused by collision of Laurasia and Gondwana lands to build Pangea Supercontinent in Late Permian/Early Triassic time-interval.By studying 130 thin-sections of Permian rocks, 36 genus (72 species) of foraimnifers, 5 genus (5 species) of red and green algae, and 2 bryozoan taxa were identified. Based on strtigraphic distribution of microfossils, 6 local biozones were distinguished which can be related to Late Permian (Late Morghabian-Djulfian) time.

Gabbroie dykes hostes in serpentinite of Dehshir-surk ophiolites have undergone hydrothermal alteration, well known as serpentinization. Serpentnization of primary minerals (Pyroxene, olivine) introuduces Ca+2 to hydrothermal fluids. These Ca-rich fluids are responsible for rodingitization of Gabbro dykes introuded in serpentinite basement.There are two distinct serpentinitization stages: dynamic and static. and it is concluded the rodingitization is a polygenic processse. The rare mineral pectolite [Na Ca2 Si3 O8 (OH)] is formed due to Na-metasomatism in the latest stage of hydrothermal processes.

The Sarvak Formation in Gachsaran well No. 55, with 844 meters in thickness was studied through 231 thin sections which led to recognition of 5 genera and 5 species of pelagic microfossils, with 23 genera and 21 species of benthic foraminifera. Four biozones were recognized as follows: 1- Favusella washitensis range zone; 2- Rudist debris zone; 3- Nezazzata.- alveolinids assemblage zone; and 4- Oligosteginids assemblage zone. As a result, the Sarvak Formation at the studied well is Late Albian to Cenomanian in age. This study also indicated that the Sarvak Formation conformably rests on the Kazh dumi Formation and disconformably overlain by the Gurpi Formation. Seven microfacies were also identified within the Formation. Based on these microfacies, the Sarvak Formation deposited mainly in an open marine, barrier and lagoon sedimentary environments. Also a regressive cycle related to the lower -middle parts and incomplete progressive cycles related to the upper part of the Formation were recognized. Based on the results, the Sarvak Formation is deposited in a homoclinal ramp. By considering the frequency of Rudist debris in the studied area and the identified microfacies, it can be interpreted that in well No. 55, the Sarvak Formation deposited in a rich oxygenic, shallow marine, and formed in a tropical condition during late Albian- Cenomanian.

The sheeted dikes form an important part of Naeen ophiolitic sequence. The petrographic studies show that the dikes are composed of basalt (dolerite), quartz dolerite, andesite, and dacite.The predominant textures are intersertal and porphyroid. The major minerals of dolerites are plagioclase, clinopyroxene and opaque. Sphene, apatite and chromian spinel are accessory minerals in these rocks. Quartz dolerites and andesites have primary amphibole and quartz too. Clinopyroxene is minor mineral in andesites, and dacites are without clinopyroxene.Clinopyroxenes are augite in composition and are Mg-rich and Ti-poor. These rocks are mostly metamorphosed by sub-sea floor metamorphism. As the result of this process, primary minerals are changed. The geochemical studies show that their magma is sub-alkalin type (low potassium tholeiite). Based on the different geochemical discrimination diagrams the samples occur in island arc tholeiite basalts field. The chondrite-normalized HFS and LIL elements show enrichment (except for Nb), but LIL elements are more abundante indicating alteration.Negative Nb anomaly is characteristic of volcanic arc magmas and can be attributed to fractionation ofNb relative to Ce and Th caused by preferential retention of Nb within the amphibole and minor phases such as titanite and rutile during dehydration and/or partial melting of the subducting plate. The chondritenormalized REE patterns of these rocks show enrichment in the HREE and depletion in the LREE.The primitive mantle-normalized REE patterns are similar to chondrite. Clinopyroxenes composition, the occurrence of chromian spinel, the normalized REE patterns and samples plotted in geochemical discrimination diagrams confirm that the magma generated these rocks is formed by high degrees of partial melting of depleted mantle. Based on all geochemical data of sheeted dikes, Nain ophiolite probably is suprasubduction zone-type ophiolite.

Tarbur Fonnations in southeast of kherameh with 700 m thickness are dominantly formed from carbonate rocks. The lower boundary with gurpi formation is conformable and the upper boundary with Sachun Formation is marked by an erosional surface. According to the lithological characteristics of the Tarbur Formation six lithological units in Kherameh area were recognaized.The study of pertrography indicates that carbonate sediments of the Tarbur Formation can be divided into 8 groups of carbonte microfacies, including: 01,02 (Open marine), B (Barrier) and Ll to L5 (Lagoon). Vertical changes in microfacies and diagram of the sea level show that sedimentation of the Tarbur Formation took place in a shallow environment. Tarbur Formation in the study area is formed in a carbonate platform (epicontinental sea), in a homoclinal ramp.

The outcrops of the Qom Formation in the southeast of Natanz with 472 meters thickness compris interbedding of thick to thin bedded limestone, marl, calcareous sandstone and sandstone. It overlies the Eocene volcanic rocks with erosional contact of nonconformity and covers by alluvial deposits. Based on the occurrence of benthic foraminifera: Lepidocyclina (Eulepidina) elephantina, Lepidocyclina (Nephrolepidina) tournoueri, Austrotrillina howchini, Operculina complanata, Neo-rotalia viennoti and Amphistegina lesson, the Chattian-Aquitanian age is determined.10 microfacies due to field work and microscopic analysis related to 4 depositional environments (open marine, bar, lagoon and tidal flat) were determined as follows: A- open marine microfacies; la- lepidocyclinidae, coralinacea wackestone-packstone, Ib- numulitidae, lepidocyclinidae, coralinacea wackestone-packstone and 2- numulitidae, lepidocyclinidae packstone. B- bioclastic bar microfacies; 3a- bioclastic grainstone, 3b- bioclastic packstone-graintone, 4- rotalidae, lepidocyclinidae grainstone and 5- rotalidae, amphisteginidae corallinacea packstone-grainstone. C- lagoon (restricted sea) microfacies; 6a- bioclastic, miliolid packstone with quartz, 6b- bioclastic miliolid wackestone-packstone with quartz, 7- bioclastic, corallinacea wackestone-packstone and 8- alveolinidae, miliolidae corallinacea floatstone. D- tidal flat microfacies; 9- bioclastic packstone- grainstonewithquartz, 10- volcanic arenite.This study reflects cyclic sedimentation due to sea level fluctuations. The sharp lithological change in 365 meters thickness, where lepidocyclinidae and nummulitidae microfacies overlap by mainly quartz packstone-grainstone could reflect fast regression of the sea and suggest a sudden fall in sea level for deposition of the upper part of the Qom Formation.

The study area is located in Central Iran Zone, 25 km southeast of Esfahan. The Upper Cretaceous sediments in the Kolah-Ghazi area can be devided into three units. The Glauconitic sandy limestone, Inoceramous limestone and marl and marly limestones of Koh-e-Shidan. Four assemblage biozones were established, throughout the Upper Cretaceous strata. Biozone I occurs in the upper part of the Glauconitic sandy limestone and the basal part of Inoceramous limestone suggesting the Late Cenomanian-Early Touronian. Biozone II is in the middle part of the Inoceramous limestone and represents the Middle Touronian. In the upper part of the Inoceramous limestone, biozone III with U. Turonian-Coniacian age can be recognized. Biozone IV (Gansserina gansseri zone) occurs in marls and marly limestone of Koh-e- Shidan and indicates the Maastrichtian age. The Maastrichtian age is considered for the rudistic limestone, based on stratigraphical position.

The Sarcheshmeh Formation (Lower Aptian) has an excellent exposure south of Agh-Darband in the easternmost part of the Kopet-Dagh Basin. It consists mostly of oolithic and fossiliferous limestones with interbedded shale and calcareous shale. The lower and upper contacts with oolithic and biogenic limestone of Tirgan and gray shale of Sanganeh Formations are conformable. Eight stratigraphic sections were measured and about 235 samples collected from limestone and shale.190 thin sections have been studied by petrographic as well as cathodoluminesce micemicroscopes to interpret the depositional and post depositional history of the Sarcheshmeh Formation. Lateral and vertical lithofacies variation in the study area shows that the Sarcheshmeh Formation, especially the limestones were deposited in tidal flat to open marine environments in a shallow marine carbonate ramp. After deposition, these limestones have been affected by different diagenetic processes including cementation, micritization, borrowing, neomorphism, compaction, dolomitization, silicification, hematitization, dissolution, fracturing and vein-fill. These processes have operated in different diagenetic environments including marine, meteoric, mixed marine-meteoric and burial during three euogenic, mesogenic and telogenic stages.

In this paper, physiochemical characteristics and evoluton of the contact zone between "Talun Tunnel intrusive body" and the "country rocks" (surrounding tuff rocks) in Central Alborz were studied. The intrusive body which is subvolcanic in texture, monzogabbroic in mineralogy and younger than Late Miocene in age, emplaced in Eocene Tuffs of Karaj Formation. The emplacements were occurred as sills and dykes and caused the development of spaced cleavage in the contact zone. Based on the physiochemical variations observed from intrusive body towards country rocks, five zones were recognized as follows: I or igneous rock zone, II or contaminated igneous rock zone, III or illite-chlorite zone, IV or altered tuff (montmorillonite) and V or tuff. This study shows that hydrothermal solutions derived from the intrusive body, initially inflicted an acidic environment on the country rocks at the contact zone. As a result, the country rocks have undergone a decrease in AI, Na, and K, while their Si increased Hydrothermal solutions decreased with time and the alkaline solutions replaced them. Effects of the the alkaline solutions are: the fixation of K and Mg and removal of Ca, the processes which promote the development of illite and chlorite in the country rocks (development of zone III). The alkaline solutions represent a marine environment which existed when zone III was forming.

The Asmari Formation, a thick carbonate succession of the Oligo-Miocene in southwest Iran, has been studied to determine its microfacies, and depositional environment. Detailed petrographic investigation led to recognition of 10microfacies including: 1) Planktonic foraminifera mudstone-wackestone,2) Bioclast, planktonic foraminifera wackestone packstone, 3) planktonic foraminifera, bioclast, nummulitidae wackestone-packstone, 4) Nummulitidae, bioclast, corallinacea wackestone-packstone, 5) Bioclastic grainstone, 6) Foraminifera, corallinacea, bioclastic packstone-grainstone, 7) Bioclast, miliolidae, neoalveolinidae wackestone-packstone, 8) Miliolids, intraclastic,bioclastic, packstone-grainstone, 9) Mudstone with shell fragments, 10) Stromatolithic boundstone.Five major depositional environments are identified in the Asmari Formation. These include tidal flat, shelf lagoon, shoal, slope and basin. The microfacies represent a carbonate platform which were developed on an open shelf without an effective barrier separating its lagoon from the sea.

Metamorphic rocks of Nain ophiolitic melange consist amphibolitic dikes, amphibolite, skarn, banded meta-chert, and succession of schist and marble. Skarns exist as a white layer between upper part of amphibolites and lower part of banded meta-cherts. Petrographical studies and geochemistry of minerals show that the major minerals of skarns are carbonate (calcite), clinopyroxene (salite), garnet (grossular-andradite), and wollastonite, and the accessory minerals are sphene and epidote. Skarns have produced by metamorphism of carbonate part of banded cherts and limestone, by a granite intrusion. Hornblenede-Plagioclase geothermometer show amphibolites and amphibolitic dikes are produced in amphibolite facies. One of the most important results of this study is presentation of this matter that "The metamorphic rocks in this ophiolitic melange are not exotic blocks, and they have produced by metamorphismof oceanic crust and covering sedimentary rocks"

The metamorphic complex of Delbar district located on 150Km southeastern Shahroud show the different metamorphic and deformation phases that may be divided into two distinctive parts based on dating relatives and metamorphic types. The older part that is similar to other Precambrian metamorphic basements in central Iran, contains a thick serie of Precambrian high-grade metamorphites including migmatized dark schists, ortho- and para-gneisses as well as ortho-amphibolites belonging to middle-upper amphibolites facles and upper sillimanite zone. The younger part is an alternation of meta-conglomerates, mlcaschists and calcschists of Jurassic that have been metamorphosed in grcensohist facies and garnet zone.The field and petrological studies show that the high-grade old meiamorphites have been intruded by numerous diabasic dykes in a tensional regitne. These broad intrusives are paraliel dykes which have increased heat flow in the crust and also metamorphosed surrounding rocks in upper silirnanite zone and consequntly migmatites and anatectic granites bad been formed. Such a condition is probably similar to tensional regimes in upper-precambriam basement in central Iran that alkaline magmas were produced as a result of crustal thinning, uplift and partial melting of upper mantle and were intruded through crust. These magmatism had been done with high-T and low-p metamorphism in the crust. The basal conglomerates (including older metamorphic and granitic grains) and calcareous shales of Jurassic have been metamorphosed into metaconglomerates and calcschists in greenschist facies.Finally, the metamorphic complex were overally affected by intense dynamic and retrograde metamorphism due to later tectonic shearing stresses. The most important evidences for the later ductile deformations include mylonitic foliations and lineations exemplified by S-C, S-C and porphyroclast tails of <5,crtypes and also mica-fish in mesoscopic scale.