JOURNAL OF SCIENCES (ISLAMIC AZAD UNIVERSITY)
Year:2006 | Volume:16 | Issue:61 (GEOLOGY ISSUE)|Papers Count:11

The Triassic rocks of the Nakhalak area with a thickness of 2701 meters are divided into three formations: Alam Formation, Baqoroq Formation and Ashin Formation which their outcrops as Nakhalak Group are bounded by two thrust faults.The Alam Formation (1298 m) with Late Scythian to Middle Anisian age consists of two facies groups; carbonate facies in the lower and upper parts of succession and the clastic facies (sandstone and shale) dominantly volcanogenic in the upper parts. Basal part of the Alam Formation consists of dolomitized oolitic limestone, oosparite, oolitic pelmicrate, lithic arenite and orthomicroconglomerate facies. Among these facies, oosparite facies shows sedimentation in platform with high energy, oolitic facies were deposited in oolitic bars environments and pelmicrate facies were deposited in limited environemts such as lagoon in continental shelf. The clastic part of the Alam Formation consists of lithic arenite, tuffaceous lithic greywacke, calclithite, interformational conglomerate and carbonate facies, which were deposited in continental slope, continental rise and abyssal plain as submarine fans.The Baqoroq Formation (1122m) with Late Anisian? to Middle Ladinian age dominantly consists of conglomerate, sandstone and shale. This formation includes lithic arenite, calclithite, orthomicroconglome rate and feldspathic greywacke facies.These facies were derived from a continental environment and deposited as alluvialfans, meandering and braided rivers.The Ashin Formation (281m) with Late Ladinian to Early Carnian? Age consists of clastic facies (dominanly sandstone and shale), which were deposited at the end of continental slope to abyssal plain, as submarine fans (distal part). This formation includes alokmical microcristaline limestone and lithic arenite facies. The Triassic rocks of Nakhlak differ completely from the shallow carbonatic and platform successions of lower and middle Triassic of Iran. The only correlative Triassic succession to these rocks is Triassic succession of Aghdarband area in northeastern Iran.

Qeshm is the biggest Iranian island in the Persian Gulf which is separated from Iranian coastline by the Clarence strait. Northwestern part of island consists of Mangrove forests in form of coastal marsh and marly sediments with grooved tidal channels. Twenty seven genera and fifty four species of benthic foraminifera were determined in the sediments of this region. It is important to note that foraminifera with coiled tests are abundant in the region mangrove forest muddy and clayly beds. Further offshore, uniserial, biserial or triserial tests exists with more abundancy and diversity .On the basis of sediment logical studies northern coasts beds, particularly in the northwestern part is muddy and clayey which is appropriate for abundancy and diversity of foraminifera with hyaline tests.

Sormeh anticline (with 50 km length and 9-14 km width) is a NW-SE anticline in the sub-coastal Fars structural zone (Zagros simple fold belt). Asmari formation and Bangestan Group are cropping out in the cores of more anticlines in the area under investigation. But, abnormally cropping out of the older formations (to Ordovician shale) in the west part of Sormeh anticline, causethat anticline had been Analyzed.Because, there is a unique outcrop of Dashtak formation that is an important cap rock in the Fars area.We have investigated the elements of fold style and folding mechanism in the West and East part of Sormeh anticline. Therefore more, uplifting of the west part, cropping out of lower Paleozoic rock units and changing the fold style are due to ramping a blind thrust in the west part of Sormeh anticline. In addition, Morphologic and seismic evidence are implying that Sormeh anticline can be considered as an active anticline.

In this study with the help of master curves of dipping beds, we try to find the dip of the layer and its elongation on depth. This study has helped us to choose best place for geotechnical borehole logging. Of course, we know that these master curves could not answer our question for depth more than about 60 meters.The further correction will be made with the help of geological data, since available curves are suitable for homogeneous and isotropic Earth. These curves will be used for dipping layer with dip angle more than 20°.Early curves were calculated for two dipping layers. The best results were found when reflection coefficient is 1 and -1.In this study we try to use these curves in the field. The field is Shorbulagh village near Karaj city for Dam construction. In this site there are three layers with 43° dip angle, sandstone and mudstone with reflection coefficient about -0.94. Four soundings were done with Schlumberger array, and the curves interpreted and the errors were shown.

Variation in mechanical properties of stratigraphic unites (change in thickness or lithology) play an important role in structural style and folding mechanism. in this study, variation of structural style in the southern Zagros fold thrust belt (Fars geological province) in the both sides of a basement high (Gavbandi basement high) has been studied based on a regional balanced transect. This study relies on field work data, existing geological maps, seismic data and well information. Neoproterozoic Hormoz salt is the basal detachment level through the studied area, however, due to lack or thinning of Hormoz salt over the Gavbandi basement high and in the western side of Razak deep seated fault, its efficiency decreased as an basal detachment and resulted in activity of other potential intermediate detachment horizons in stratigraphic column (such as Triassic evaporates and shales, Dashtak Formation) during folding. This intermediate detachment level accommodated the shortening in different ways and lead to an obvious variation in structural style in the both sides of Gavbandi paleohigh.

In order to analyze the fractures of the iron stone of Se-chahun, the structures of the considered area has taken and after provision of surface map of the area in order to study these structures, contour diagram and rose diagram supplied and studied.As general this investigation showed that four fault system influenced on the rock units of the area. The trend of four system included N-S, E-W, NW-SE and NE-SW. The systems caused by activity of N-S faults (Posht-e-Badam and Kuhbanan fault). This investigation determined that rotation effect of central Iran and block faulting observed at smaller scale in suburb of Se-chahun mine.

Thrust fronts have different structural styles and they have classified to the two main types by some researchers. In this paper, thrust fronts of the Alborz-Central Iran border zone from the east of Varamin to the east of Semnan have introduced and classified.Therefore, north Semnan thrust front has distinguished as a buried thrust front (type 2) that end in zones of high strain. North Sorkheh and Garmsar thrust fronts have distinguished as weakly emergent thrust fronts that situated in the Overstep thrust sequences. Finally, south Pishva thrust front has distinguished as a strongly emergent thrust front that situated in the Piggyback thrust sequence.

The Fahlian Formation is studied in two stratigraphic sections that are named, Kuh-e Gadvan and Kuh-e Ab Siah. Based on lithostratigraphic characteristics, the Fahlian Formation is divided into six lithostratigraphic units. Biostratigraphic limits of the Fahlian Formation are determined. Foraminiferal and algal remains constituents of the studied section are listed below:pseudocyclammina lituus Yokoyama, P.gerigi Henson, Pseudochrysalidina arabica, Henson, P.conica Henson, Trochlina alpina , Leupold T.conica Schlumberger, T arabica, Schlumberger, T.sp., Dorothia sp., Gaudyrina sp., Marssomella cf trochus Cushman T.sp., Calpionella alpina Lorenz, Conoroboides sp., and calcareous algae in eluding: Salpingoporella annulata Crozzi, S.sp., Lithocodium sp., Actinoporella sp., and Litusepta sp. Foraminiferal studies indicate that biostratigraphic limits of the Fahlian Formation sections are Briasian to Hauterivian. Also six type microfacies in Kuh-e Gadvan and three type microfacies in Kuh-e Ab Siah are identified in the Fahlian Formation.

The Razan (Hamadan) area is located about 300 Km of southwest of Tehran. The southern part of this area is belonging to Sanandaj-Sirjan and northern part belongs to Central Iran zones. The marine deposits of Oligo-Miocene (Qom Formation) are well distributed in the area. Lavas and volcanoc1astics are important parts of Qom Formation. These parts exposed in vast bond which has a SE-NW direction like general Zagros zone trend. Petrological study of lavas in Qom Formation is the most important aim in this research and it's based on field observation, petrographical and geochemical (XRF, Isotopic geochemistry and SEM analyses) study. This research show that extrusive rocks of studied area are dacite-ryodacite, andesite, trachyandesite, homblend andesite, basaltic andesite and trachybasalt. It also revealed that different phenomena like contamination and probably magma mixing had affected on extrusive rocks magma formative.

Aliabad area is located northeast of Qom. Sedimentary rocks with Eocene, Oligocene and Miocene ages and quaternary sediments are present. Most of the area covered by pyroclastic and volcanic rocks which are affected by low metamorphism and alteration. Pyroclastic rocks are mainly tuff and ignimbrite and volcanic rocks are intermediate to basic olivine basalt, basalt andesiticbasalt and tracky-andesite. An intrusion with dykes and sills intruded Eocene pyroclastic rocks. Considering the geochemical diagrams, volcanic rocks are mainly sub-alkaline (calc-alkaline) type, but some samples show tholeiitic features. Microscopic studies and chemical analyses show magma contamination. Based on variety of rocks, basic to intermediate rocks are possibly formed from fractionation of basaltic magma with mantle source. However, based on presence of high volume of intermediate rocks and ignimbrite in the area, it is possible that they formed during partial meeting of the crust. The basic rocks formed in active continental margin.