Upper Carboniferous and Permian biostratigraphy of the Middle Tianshan

Abstract

The biostratigraphic study of the upper Carboniferous and lower Permian stratotype sections in the Middle Tianshan of Kyrgyzstan enable us to identify foraminifera complexes that characterize certain intervals of the section, defined as foraminifera zones. In stratigraphic interval from the Kasimovian to Asselian stage, we distinguish seven foraminifera zones as follows: 1. Triticites komansuensis — Triticites procerulus, 2. Schwageriniformis arpaensis — T. turkestanensis, 3. Jigulites corpulentus — Daixina porrecta, 4. Daixina vasilkovskyi — Quasifusulina kodzhagulica, 5. Daixina (B.) bosbytauensis — Pseudodaixinoides kacagaricus, 6. Occidentoschwagerina alpina, 7. Schwagerina moelleri — Grozdilovia (?) fecunda. These zones were distinguished based on the study of 350 species of fusulinides, including 65 new endemic species (Djenchuraeva, Getman, 2007, 2010). Occurrence of endemic species in the zonal complexes hampers the correlation of these zones with coeval strata in other regions. However, it allows one to reconstruct sharp changes in the facial conditions of Foraminifera’s existence which resulted from increasing isolation of the eastern part of the Turkestan ocean. New endemic species are characterized by common features, such as small initial chamber, close coiling of the helix in the internal rotations and strong folding of septa in higher forms. Sedimentological observations help to restore depositional environment of the basin in the eastern part of the Middle Tien Shan. Djenchuraeva A. V. and Gonchar A. D. (2001) describe shallow litofacies and tempestites in the upper Carboniferous and Lower Permian sediments of this region. The study of the full composition of foraminifera complexes allows to compare them with the zonal subdivisions of various regions of Central Asia, Urals, Russian Platform and Donbas.