Llandovery fauna of Iran during the post-extinction recovery (original) (raw)
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Gondwana …, 2011
Early Silurian (Aeronian) carbonate platform deposits of the lower Niur Formation of east central Iran yield an ostracod fauna of fourteen species dominated by podocopes with rare palaeocopes and binodicopes. The podocope-rich fauna is unusual in that Early Palaeozoic carbonate platforms are typically dominated by palaeocopes. Despite its mid-palaeolatitude peri-Gondwanan setting and isolation from low palaeolatitudes, the ostracod assemblage of the lower Niur Formation shows striking affinities to species-level with Late Ordovician and Early Silurian ostracod faunas of palaeo-equatorial Laurentia. Biogeographically the lower Niur Formation ostracod fauna also shows species- and genus-links with Late Ordovician and Early Silurian faunas of low-palaeolatitude (0°–30°S) Baltica and mid palaeolatitude peri-Gondwanan Uzbekistan, dispelling the notion of strict endemism for Early Silurian ostracods. Two new species Bulbosclerites jamshidis sp. nov. and Steusloffina fravashi sp. nov. are described.► Silurian ostracods of Iran yield many survivors of end Ordovician glaciation. ► They show repopulation of high latitudes by low latitude tropical fauna. ►They also dispel the notion of strict endemism for Early Silurian ostracods.
FAUNAL CHANGE NEAR THE END-PERMIAN EXTINCTION: THE BRACHIOPODS OF THE ALI BASHI MOUNTAINS, NW IRAN
The Julfa Formation in the Ali Bashi Mountains, northwest Iran, is very rich in brachiopods, particularly in its lower part, whichhas been dated by fusulinids and conodonts as Wuchiapingian in age. The brachiopod fauna described hereinhas been collected alongthe Main Valley section of the Ali Bashi Mountains, several hundred metres awayfrom the historical sections described in the 1960’s and 1970’s. It comprises 39 species of the orders Productida, Orthotetida, Orthida, Rhynchonellida, Athyridida, Spiriferida, and Terebratulida, most of which are known in the coeval successions of Transcaucasia, Alborz Mountains in north Iran and in South China, confirming the Wuchiapingian age indicated by other proxies. A few of the brachiopod taxa range up into the ChanghsingianParatirolites Limestone. The shale and marly limestone at the base of the formation are dominated by semi-infaunal productids, that are progressively succeeded near the top of the lower part of the formationby a more diverse range ofpedicle attached and cemented taxa,suggesting a shallowing upward trend and a shift to higher nutrient-substrates in more turbulent waters. The successive deepening trend recorded in the upper part of the Julfa Formation and in the overlying Ali Bashi Formation is very unfavourable for the brachiopods and only a few species survive, represented by small sized pediculate taxa that thrive on hardgrounds.
2003
Acritarchs from the Shirgesht, Ghelli and Niur formations were used to determine the age of these rock units and to assess their paleogeographic importance. These formations yielded 55 palynomorph taxa (54 acritarch species and 1 cryptospore species) permitting the recognition of eight biozones (palynozones). The zones I - III represent the Early Ordovician (Tremadocian-Arenigian), zones IV-VI indicate Middle-Late Ordovician (Llanvirian-Ashgillian) and zone VII suggests the Early-Middle Silurian (Llandoverian- early Wenlockian). The presence of genera such as Arbusculidium, Striatotheca and Coryphidium in the Early Ordovician sediments of the Shirgesht Formation from the eastern Central Iran suggest, that the Iranian Platform was part of Peri-Gondwanan Paleo-continent, possibly along the southern shore of the Paleo- Tethys Ocean during the Early Ordovician . Comparison of acritarch taxa from the Ghelli (Middle-Late Ordovician) and Niur (Early-Middle Silurian) formations with those f...