Tectonics
Zeynab Taslimi; Abdollah Saidi; Mehran Arian; A. Solgi; Manouchehr Ghoreshi
Abstract
The Alborz Mountains has been separated the subsiding Caspian Basin from the foreland basin of Central Iran. This mountain range from east to northwest, has changed greatly in structural trend formed spirally. Two orogenic phases, Cimmerian and Alpine events caused more changing in sedimentary basin ...
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The Alborz Mountains has been separated the subsiding Caspian Basin from the foreland basin of Central Iran. This mountain range from east to northwest, has changed greatly in structural trend formed spirally. Two orogenic phases, Cimmerian and Alpine events caused more changing in sedimentary basin of Palo Tethys and Neotethys and it caused the complexity of abundant structural in other way too. The aim of this research is to investigate and analysis of existence structures in east central Alborz from northwest of Damghan (South of Toyeh) to South of Sari (North Alborz fault). The Structural features Analysis indicate that the Alborz Mountains are a fold and thrust belt. During the intense shortening of Alborz crust in the studied area the initial model of folds have been modified or destroyed. Some of these folds could take place in flexural flow folds or Drug folds classes since one limb of folds on the surface of low-angel thrust faults was thrusted recumbently. The thrust faults with south and north dipping is the main controller for variety structures in this part of Alborz. Based on geological and structural properties, construction of folding structures initiated during the Alpine orogeny since the late Eocene (37 million years) and the most shortening and faulting had occurred during at the Late Miocene. Data presented here demonstrate that shortening percent in the study area of Alborz Mountains is about 36.27% and the Rate of Shortening is estimated about 0.93 mm/y.
S. H. Hashemi; M. Fahimi
Abstract
The Upper Devonian sequences in vicinity of Darvar, southwest Damghan comprise alternation of conglomerates, quartzites, sandstones, siltstones, shales, with fossiliferous limestone intercalations unconformably overlying the Ordovician strata and gradually preceding carbonates of the Lower Carboniferous ...
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The Upper Devonian sequences in vicinity of Darvar, southwest Damghan comprise alternation of conglomerates, quartzites, sandstones, siltstones, shales, with fossiliferous limestone intercalations unconformably overlying the Ordovician strata and gradually preceding carbonates of the Lower Carboniferous Mobarak Formation. Diverse biota embracing brachiopods, trilobites, fish, gastropods, corals, echinoderms, and conodonts in conjunction with well preserved palynomorphs, in descending order of abundance, of both terrestrial and marine origin occur in the Upper Devonian strata (Geirud Formation) of Darvar, southwest Damghan. Scolecodonts rarely occur in the material studied but no representative of Chitinozoans encountered. Based on the known stratigraphic distribution of taxa such as Cymatiosphaera perimembrana, Chomotriletes vedugensis, Deltotosoma intonsum, Papulogabata annulata, Tornacia sarjeantii, Unellium lunatum, Unellium piriforme, Retispora lepidophyta, Geminospora lemurata, Retusotriletes rugulatus, Grandispora cornuta, Grandispora sp. cf. G. gracilis the Geirud Formation is attributed to the Late Devonian (Frasnian-Famennian). Occurrence, in the material studied, of microphytoplankton cysts with relatively thin eilyma and ±circular, psilate or sculptured vesicle indicates deposition in a shallow, marginal marine depositional setting. Presence of Geminospora lemurata in majority of the samples refers to the occurrence of progymnosperms and that of poorly preserved Lepidodendrales to that of lycopodophytes in contemporaneous land vegetation. Affinity of sporae dispersae in the Geirud palynoflora indicates that fern allies such as Equisetopsida, Lycopodopsida, Rhyniopsida, and Progymnosperms were represented in the land vegetation. Relative abundance of Geminospora lemurata and spores attributed to lycopodophytes imply domination of the land vegetation by lycopodohytes and progymnosperms.