Rock beds containing plant macrofossils of Norian in Alborz region belong to two stratigraphic units of Lalehband and Shahmirzad. The same beds in Kopeh-Dagh area belong to Mian-Kuhi Formation and in Central Iran belong to Qadir submember in Tabas region and Dehroud member in Kerman region. In general, plant diversity and vegetative cover during the Norian stage is less than Rhaetian especially Jurassic (Shemshak group) and the highest plant diversity of Norian in the Alborz basin is reLated to the phyllum of Pteridospermophytes (seed ferns) and in the Central Iran basin is reLated to the phyllum of Pteridophyta (ferns) indicating the higher humidity of the mentioned time in Central Iran basin and the drier climate in Alborz basin. The highest diversity of vegetation in Norian sediments throughout Iran belongs to the seed ferns (Pteridospermophyta) and the lowest diversity belongs to Ginkgophytes so that they comprise 32% (one third of the vegetation) and 6. 5% of the total vegetation, respectively. Plant-covered areas throughout Alborz were interconnected during the Norian period and there was no extensive separation between them. The plant macrofossils assemblage in both Alborz and Central Iran basins confirms the relatively humid subtropical to tropical climate for the Norian but less humidity compared to the Rhaetian. Also, the vegetation of Norian in Alborz was less dense and scattered than Central Iran during Norian.

The Shemshak Group is well-exposed in Ramsar coal-bearing region and consists of four formations,Ekrasar, Laleband, Kalariz and Javaherdeh. The Laleband Formation lies conformably and gradationally on top of Ekrasar formation and its upper contact is conformable and sharp under Kalariz formation. It contains scattered plant macrofossils of Norian-Rhaetian age. The studied section contains well-preserved and scattered plant macrofossils belonging to three orders as Equisetales, Filicales and Pinales. Based on the occurrence of Neocalamites sp. cf. N. carcinoides, Dictyophyllum sp. cf. D. exile, Clathropteris meniscoides and Cycadocarpidium erdmani and stratigraphic position of fossil bearing layers, Late Norian –,Early Rhaetian age is suggested for the studied beds.

In this research, gray, green, red to cream limestone, shale and marly deposits of the Julfa, Alibashi and lower part of Elikah Formation at the Zal stratigraphic section, NW Iran, with 67.20 meter thickness have been studied based on conodonts. This investigation is led to identification of 27 species and 4 subspecies belong to 5 different genera of conodonts while a proposed new subspecies Clarkina leveni zalensis n. sub sp. belonging to the species Clarkina leveni have been described. Also, 18 conodont zones with the age of Wuchiapingian – Griesbachian have been determined. Amongst them, 5 biozones belong to Wuchiapingian, 10 to Changhsingian and 3 to Griesbachian whereas the Late Permian extinction horizon is located on the upper surface of the Paratirolites Limeston last bed like other sections in the Alibashi Mountains re gion. In addition, Wuchiapingian – Changhsingian boundary is located at the Julfa to Alibashi formations boundary and the Permian – Triassic boundary placed at the gray calcareous parts of the lower Elikah Formation, +0.90 m above the extinction horizon. Unlike some recent entries, the boundary between Alibashi and Elikah formations are continuous due to the presence of two conodont zones Clarkina meishanensis –Hindeodus praeparvus As. Zone and Merrillina ultima – Stepanovites? mostleri As. Zone in the marine shaly Araxes member and lower carbonate part of the Elikah Formation, occurrence of small orthotetid brachiopods, bellerophontid gastropods and numerous Bairdiidae ostracods in this shaly member even several preceding geochemical and isotopic studies.

The Upper Triassic Nayband Formation is widely exposed in the Tabas subzone, East Central Iran. This formation is 1410 meters thick, mainly comprises sandstone, sandy limestone, marl, coalificated shale (Coal seam) and dark shale in Parvadeh area. This study tries to reconstruct the hydrocarbon production potentiality, organic geochemistry, kerogen type, thermal maturity and recognition of depositional condition of the Nayband Formation. Totally 86 samples (coal seams and dark shales) were collected. These samples were analyzed by Rock-Eval type VI. Geochemical analysis results revealed that TOC content is more than 4 Wt% in the coalificated shales and in the dark shales is less than 4 Wt%. Parameters such as S1, S2, S1+ S2 suggest poor hydrocarbon production. Other parameters such as HI suggest poor hydrocarbon production potential (coalificated shales) to gas prone source rock (dark shales). Results also revealed that the organic matter mainly contain type IV kerogen in the coalificated shales and predominately comprises kerogen types III and IV in the dark shales. Vitrinite reflectance of the coalificated shales (0.84-1.12 %) indicate that the coalificated shales are at the mature stage (enrichment of oxidized organic matter indicates poor hydrocarbon production). Organic facies of this rock unit indicates that these sediments predominately comprise organic facies types D and CD which imply highly oxic to oxic conditions during the deposition. Based on HI and TOC parameters, majority of these sediments were deposited during relative sea-level fall.

Nayband Formation is composed of sandstone, coal bearing shales, siltstone, and fossiliferous limestone in the southwest Tabas section, east central Iran. In this section, it is 1410 m in thickness and Late Triassic in age. A divers trace fossils have been found in the middle parts of sequence as 400-600 m. These trace fossils include Lockeia isp., Palaeophycus tubularis, Palaeophycus striatus, Planolites beverleyensis, Rhizocorallium isp., Rosselia isp., and cf. Treptichnus isp. This ichnoassemblage is attributable to Cruziana ichnofacies with presence of Lockeia isp., Rhizocorallium isp., and, Rosselia isp. This part of Nayband Formation was deposited in low energy conditions below fair-weather wave base.

Vitrinite reflectance (%Ro), and well log data of the Permo-Triassic and the Mesozoic sequences including Karro, Hamanlei, and Urandab Formations. Burial history and level of thermal maturity of the Bodle-1 well, the Calub-1 well and the Hilala-2 well were modeled based on the calibration of measured %Ro and Tmax against calcuLated %Ro model. The calcuLated Total Organic Carbon (TOC) content from the well log data compared with the measured TOC from the Rock-Eval pyrolysis in the three mentioned wells is shown to match against the shale source rock. The total organic carbon (TOC) content value ranged from 0. 48 to 4. 24 wt % while the S1 and S2 values ranged from 0. 05 to 0. 76 (mg/g) and 8. 52 to 27. 88 (mg/g) respectively. Hydrogen index (HI) versus oxygen index (OI) plot has shown that the organic matter is predominately made up of type III kerogen (gas prone) while Tmax and HI indicated mixed type II/III kerogen (25% of Urandab Formation, 40% of Bokh Formation and 15% of Hamanlei and Adigrat Formations). Tmax was assessed from vitrinite reflectance (Ro) readings for Bodle-1, Calub-1 and Hilala-2 wells showed an average vitrinite reflectance values in the range of 0. 5-1. 4 VRo%, 0. 35-1. 08 VRo %, 0. 55 – 0. 69 VRo % respectively. The developed burial history models have revealed that Bokh Shale hydrocarbon generation has been started during lower Jurassic, and presently hydrocarbon generation has been started within the “ oil window” while Urandab Shale is immature to fairly mature.

The Nayband Formation in North of Isfahan includesfive Members: 1- Gelkan Member (marl and sandstone), 2- Bidestan Member (sandstone and reefal limestone), 3- Howz- e- Sheikh Member (marl and sandstone), 4- Howz- e- Khan Member (marl and reefal Limestone) and 5- Qadir Member (marl and sandstone). The biostromal limestones of Bidestan and Howz-e- Khan Members represent a typical known key bed in North of Isfahan. In Bidestan and Howz-e- Khan Members (NaybandFormation), coral reefs grow up and their distribution are significant in the biostromal limestone of Bidestan and Howz-e- Khan Members of Nayband Formation.Twelve genera and 31 species of Scleractiniancorals were recognized in thesereefal members. They included: Reimaniphylliidae, Margarophylliidae, Coryphylliidae, Cyclophyllidae, Astraeomorphidae, Pamiroseriidae, Stylophyllidae and Actinastraeidae families. According to the field observations and evidences, laboratory studies and analysis, measurements of the coral size and the destroyedepitechaof thecorals, it could beguessed that Scleractinian corals survive below the storm wave base (about 20 meters depth) but they tolerated many storms. Morphology of Scleractinian corals of Late Triassic sea (North of Isfahan) indicatesinadequate living conditions and high energy environment. Corals have major roleinreconstruction of Paleoenviromentofthe LateTriassic unitsofthe North of Isfahan (Nayband Formation) in Dizlusection.

The study area is situated in the Middle part of the Tabas Block. It contains outcrops of rocks that formed along longitudinal faults in Early Cimmerian orogenic phase. The basin subsided along these faults from the Late Triassic to Early Cretaceous, which include two sedimentary cycles. A sedimentary cycle, reLated to Upper Triassic to Bajocian is known as Shemshak group. Another sedimentary cycle, reLated to Bathonian to Upper Jurassic, is known as MAGU group. The Cretaceous rock units include red coarse-grained sandstone, at the base changing upward into red gypsifferous marl, rudist limestone and conglomerate, which deposited in a shallow marine environment. Subsidence analysis is applied to geologically disconnected objects in a manner that departs from its traditional use in basin analysis. However, as it introduces quantified data on the behavior of the crust in response to tectonics, it was shown to be an efficient tool in sorting out the major events amongst various local evidences for crustal instability. Based on the subsidence curves plotted for tectonic domain of the Tabas Block , the major obtained results include: - subsidence curves shown a relatively high subsidence rate in the Upper Triassic to the Middle Cretaceous, that coupled with rifting environment in this time; - this rifting was rapidly ceased in the Late Cretaceous to form Aulacogen (Failed Rift) and caused to generate oceanic crust and overriding of Sabzevar-Nain-Baft Ophiolites in this time; - subsidence rate in this part of Tabas Block was increasing towards the west and the north.

Dioritic plutons and pinkish alkali-feldspar granitic dikes of KaLateh area (northwest of Khur city) intruded in Neoproterozoic basemental of Jandagh-Arousan complex. Field observations, petrography and geochemical studies indicate that these intrusive rocks have I-type nature and belong to medium-high K calc-alkaline granitiods and also have genetically relationship with each other. Their parental magmas produced by partial melting of metasomatized mantle wedge which was located above the subducted Neotethyan oceanic slab. The mentioned magmas generated in an intracontinental back arc extensional setting in relation to the subduction of oceanic Neotethys slab. U-Pb dating results on separated zircon from dioritic and alkali-feldspar granitic rocks indicated 213. 9 ± 1. 6 to 221. 16 ± 1. 6 Ma interval age (corresponding to Late Triassic). These igneous rocks are indications of magmatic manifestations of Early Cimmerian Orogeny.