Endemic Silurian ostracod faunas of the Southern Tien Shan, Central Asia

Abstract

The overall occurrence, composition, stratigraphic distribution and palaeobiogeographic and biostratigraphic significance of ostracod faunas in the Silurian of the Southern Tien Shan in Uzbekistan and Tajikistan, central Asia is, for the first time, documented herein. The faunas are diverse in each of the four Silurian series, with podocopes, palaeocopes and mydocopes present and podocopes dominant throughout. The faunas are species rich, with some 300 ostracod species recorded, predominantly from shallow water mostly shelf and shelf slope carbonates of various kinds. The ostracod faunas are dominantly (95%) endemic to the area, and the endemicity is apparent throughout the Silurian. The occurrence of benthic podocope and palaeocope ostracods endorses the palaeogeographic model of a close assembly of several microcontinental blocks (e.g., Karakum-Tadjik, Uratyube-Osh, Kyzyl-Kum/Alai) associated with a putative (Turkistan) Ocean during the Silurian. There is also evidence, from the co-occurrence of some ostracod species, that supports tectonic models indicating proximity of the Urals (‘Urals Ocean’) to central Asia (areas bordering the ‘Turkistan Ocean’) during the Silurian. Ostracods provide markers for dating and correlation at various stratigraphic levels of the Silurian within and between localities across central Asia. Ostracods are also valuable in intercontinental biostratigraphy and correlation in the Ludlow Series, using cosmopolitan myodocope species that occur in deeper slope facies in Uzbekistan.