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.
