S. Hemati; M. Taherpour Khalil Abad; A. Ghaderi; A. R. Ashouri
Abstract
Micropaleontological study on the carbonate successions of the Tirgan Formation at the Taherabad village and Eshlir anticline stratigraphic sections is led to identification of various taxa of the calcareous algae belong to the families Dasycladaceae, Triploporellaceae, Udoteaceae, Solenoporaceae and ...
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Micropaleontological study on the carbonate successions of the Tirgan Formation at the Taherabad village and Eshlir anticline stratigraphic sections is led to identification of various taxa of the calcareous algae belong to the families Dasycladaceae, Triploporellaceae, Udoteaceae, Solenoporaceae and Gymnocodiaceae and also some specimens of small Gorgonacea. Based on the biometric measurements of morphological features, 16 genera and 20 species from the Taherabad section and 12 genera and 16 species from the Eshlir section have been recognized. Moreover, Permocalculus minutus and Permocalculus? halimedaformis have been found for the first time in the Tirgan Formation. Permocalculus? halimedaformis was introduced from the Minis Valley in Romania for the first time and its finding in this research is the second report around the world. According to this new finding, its geographic distribution is being extended more than 2800 km eastward on the northern margin of the Tethys ocean.
S.Z Pourheidar; A Mahboubi; M.H Mahmudy Gharaie; S.R Moussavi Harami
Abstract
The Mozduran Formation in west of the Kopet-Dagh basin, NE Jajarm, is mainly composed of dolostone in top and base, and mudstone to grainstone limestones in the middle parts of Cheshme-Khan section. This formation in the Qezel-Tapeh2 well is composed of alternative limestone and shale layers. Based on ...
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The Mozduran Formation in west of the Kopet-Dagh basin, NE Jajarm, is mainly composed of dolostone in top and base, and mudstone to grainstone limestones in the middle parts of Cheshme-Khan section. This formation in the Qezel-Tapeh2 well is composed of alternative limestone and shale layers. Based on the facies studies, four carbonate facies associations (open marine, barrier, lagoon and tidal flat) have been identified, including fifteen carbonate microfacies and two siliciclastic lithofacies. It is interpreted that the Mozduran Formation in this area were deposited in a homoclinal ramp of a carbonate platform. The sequence stratigraphy analysis led to distinguish five depositional sequences in the Cheshme-Khan section and four depositional sequences in the Qezel-Tapeh2 well. The lower boundary of the 1st sequence (paleosol layar in the Cheshme-Khan section) and the upper boundary of the latest sequence (continental deposits) of both sections are a "type 1" sequence boundaries, but other boundaries are interpreted to be a "type 2" sequence boundaries. The relative sea-level curve of the study area comparing to the global sea-level curve, shows a relatively correlation and some differences can probably be related to regional tectonic setting of the Kopet-Dagh basin due to subsidence along the longitudinal faults and sediment loading.
Alireza Shahidi; E. Barrier; M.-F. Brunet; A. Saidi
Abstract
In northern Iran the Eo-Cimmerian orogeny resulting from this collision is associated with a regional unconformity and a major change in sedimentation. From Norian to middle Bajocian (Shemshak group), 030° trending extension is indicated by syndepositional normal faults. We assign this extensional ...
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In northern Iran the Eo-Cimmerian orogeny resulting from this collision is associated with a regional unconformity and a major change in sedimentation. From Norian to middle Bajocian (Shemshak group), 030° trending extension is indicated by syndepositional normal faults. We assign this extensional tectonics to the rifting phase preceding the oceanic opening of the South Caspian Basin. Dalichai and Lar formations, late-Bajocian to Neocomian in age, conformably cover the Shemshak in central Alborz. They are contemporaneous with the opening of the South Caspian marginal basin. In Alborz, the lower part of the Cretaceous sequence is associated with E-W to WNW-ESE trending normal fault systems associated with magmatism related to an N-S to NNE-SSW trending extension during this period. The Cretaceous-Palaeogene boundary is marked by a major regional unconformity. This unconformity is related to a major inversion of the southern margin of the South Caspian basins. During the early-middle Eocene, southern Alborz is characterized by a rapid subsidence of the Karaj basin. Syndepositional E-W to WNW-ESE trending normal faults are common in the Karaj Formation. They are associated with a well-determined N-S to NNE-SSW extension. We assign the Karaj basin to a back-arc basin related to the NE subduction of the neo-tethyan oceanic lithosphere beneath the southern margin of Eurasia.
M. Vahidinia; A. Sadeghi; A. Shemirani; A-A. Aryai; M-A. Adabi
Abstract
The Kopet Dagh basin was formed during and after the collision of Turan plate with Iran plate before late Carnian (about 225 m.y. ago). It is located in the northeast of Iran and has a WNW to ESE trend. Neyzar Formation is composed of siliciclastic sediments and sandy shale and sandy limestone. This ...
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The Kopet Dagh basin was formed during and after the collision of Turan plate with Iran plate before late Carnian (about 225 m.y. ago). It is located in the northeast of Iran and has a WNW to ESE trend. Neyzar Formation is composed of siliciclastic sediments and sandy shale and sandy limestone. This unit is widespread in the east and northeast parts of the basin. To determine the stratigraphy, microfossils, microfacies and depositional environment of Neyzar Formation, three stratigraphic sections were selected and measurement and detailed sampling carried out on each of them. These sections from east to west are as fallows :
1) Tang-e Neyzar (Neyzar gorge) section
2) Tang-e Chahchaheh section
3) Jalil abad section
In the previous studies, the base and top boundaries of Neyzar Formation with Abtalkh and Kalat Formations were reported conformable and transitional (Afshar Harb, 1373). However, according to present investigations in eastern regions, lower boundary of Neyzar Formation with Abtalkh Formation in sections 1 and 2 are disconformable (as a Paleosol). This boundary in the section 3 is conformable and transitional. The upper boundary of Neyzar Formation with Kalat Formation in 1, 2 and 3 sections are disconformable (as a paleosoil).
Two types of facies were identified based on micropaleontologic and petrographic studies: 1) Siliciclastic facies, 2) Carbonate facies. Based on microfacies studies it seems that the siliciclastic parts of Neyzar Formation was deposited in a lagoonal-barrier island environments and the carbonaceous parts in a shallow carbonate platform (ramp type).
In most of the published reports and articles Neyzar Formation was introduced as low fossil bearing unit with no index–fossil. The age of this formation was determined only by the basis of its stratigraphical situation, but in the present investigation, in addition, 41 genera and 30 species of microfossils have been identified for the first time from index fossils such as:
Orbitoides apiculata, Orbitoides tissoti, Lepidorbitoides sp., Siderolites calcitrapoides, Pseudosiderolites vidali, Abathomphalus mayaroensis.
These fossil assemblages suggest the Maastrichtian, especially Late Maastrichtian age for Neyzar Formation.
