Document Type : Final File
Author
Institute of Petroleum Engineering of Tehran University, Tehran, P. O. Box, 11365-4563, Islamic Republic of Iran.
Abstract
Well-preserved miospore assemblages are recorded from the Late Ordovician (Katian-Hirnantian), Ghelli Formation in Pelmis-gorge at the north-eastern Alborz Mountain The palynomorphs were extracted from siliciclastic deposits which are well-dated by using of marine palynomorphs (acritarchs and chitinozoans). The encountered miospore assemblages consist of 14 genera (28 species: 26 cryptospores and 2 trilete spores). Six new cryptospore taxa are described: Rimosotetras punctata, Rimosotetras granulata, Dyadospora asymmetrica, Dyadospora verrucata, Segestrespora iranense and Imperfectotriletes persianense. The present findings contribute to improving knowledge of origin and onset of development of vegetative cover during the Late Ordovician. The recovery of diverse and abundant cryptospores in the Late Ordovician (Katian-Hirnantian) Ghelli Formation are probably related to increasing input of land-derived sediments during the global sea-level fall linked to the Late Ordovician glaciation, and tolerance of the primitive land plants in a wide range of climatic conditions. These miospore taxa were produced by earliest primitive land plants which probably grew close to the shoreline and washed in from the adjacent areas and produced high amount of miospores. The associated marine palynomorphs consist of acritarchs (13 genera and 18 species), chitinozoans (9 genera and 10 species), prasinophycean algae, scolecodonts and graptolite remains which are not discussed in detail herein. The established chitinozoan biozones of this part of Palaeozoic sequences are Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata and Spinachitina oulebsiri, suggesting the Late Ordovician (Katian-Hirnantian). These chitinozoan biozones are well-known only in peri-Gondwanan Domain, indicating that the study area has been part of this palaeo-continent during the Late Ordovician.
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