Conodonts, radiolarians and ostracodes in the Permian E-Lert Formation, Loei Fold Belt, Indochina Terrane, Thailand

Conodonts are rare in the Permian carbonates of Indochina but abundant conodonts and ostracodes have been obtained from turbiditic limestones of the Permian E-Lert Formation along with radiolarians from overlying cherts, all deposited on the margins of the interplatform Nam Duk Basin. Conodonts are typically Tethyan and are very similar to faunas from Sicily and south China. They includeHindeodus gulloides,Pseudohindeodus oertlii,Mesogondolella siciliensisandSweetognathus subsymmetricuswhich indicate a probable late Kungurian – Roadian age range although a Wordian age cannot be excluded.M. siciliensis, which has a high blade and small cusp supposedly typical of warm-water conodonts, is found in deep (<500 m) carbonate turbidites in Thailand and in very deep deposits in Oman and Sicily, but generally not in shallow-water tropical limestones in Thailand, Oman and Sicily. The chert sequence yields a radiolarian fauna consisting of 11 confidently assigned species of whichAlbaillella asymmetrica,A. sinuata,Tormentum delicatumandLatentifistula patagilateratasuggest a latest Kungurian – earliest Roadian age, deposited at a palaeodepth ofc.500 m. Ostracodes consist of 16 genera and 23 species which belong toShivaella,Paraberounella,Carinaknightina,Paraparchites,Shemonaella,Bairdia,Cryptobairdia,Bairdiacypris?,Spinocypris,Pseudobythocypris,Baschkirina,Microcheilinella,Basslerella,PolycopeandCyathus, of whichShivaella elertensis sp. nov.Chitnarin is newly described. The ostracodes are a palaeoecologically mixed assemblage comprising external platform and deeper-water forms, suggesting that the limestone turbidites were deposited on the proximal part of the slope.Cyathus caperataandC. ellipticashow a palaeobiogeographic link to south China.

Late Paleocene radiolarian fauna from Tibet and its geological implications

A diverse, abundant, and well-preserved radiolarian fauna in Jiazhu, Zhongba County of Tibet, in the western sector of Yarlung Zangbo Suture Zone, is assigned to a late Paleocene radiolarian zone, the Buryella pentadica interval zone, spanning 59–56.5 Ma. Regionally, a late Paleocene basalt block in the bathyal–abyssal siliceous mudstone and graywacke yielded an age of 59.1 Ma (zircon SHRIMP U–Pb). The late Paleocene radiolarian fauna, the tectonic attribution of the radiolarian cherts and the basalt block indicate that oceanic crust persisted in the Zhongba area until the late Paleocene and the initial collision between the Indian and Eurasian plates post-dates the late Paleocene. It is inferred that the Neo-Tethys transformed into a remnant oceanic basin in the late Paleocene, at the terminal stage of the oceanic crust subduction, and the closure of the remnant oceanic basin in the studied region took place after the late Paleocene. In contrast to the previous investigations, we suggest that there was a remnant oceanic basin to the west of the Saga area and a foreland basin to the east of Saga in southern Tibet during the late Paleocene. We argue that the closure of the Neo-Tethys progressed from east to west.