DEVONIAN IN MONGOLIA

Abstract

Mongolia contains extensively developed Devonian marine deposits, which are characterized by latitudinal facies zoning. At the present time, R. Ye. Alekseyeva has established the following horizons in the Lower and Middle Devonian of Mongolia: the Bortegskiy (Lokhkovian), Bigerskiy (Praguian), Chulunskiy (Emsian), Tsagan-Khalginskiy (Emsian-Eifelian) and Tsagan-nur (Givetian). The zonal subdivision of the Lower Devonian carbonate and elastic sections that cannot be correlated on the basis of fauna was done separately, and their parallelization was mutually controlled by historical-geologic and biostratigraphic data. The first were the correlation levels corresponding to the changes in regressive and transgressive cycles; the second were the data on the correlation of the sections in Mongolia, the Gornyy Altay and the Salair regions. The relation of the regional zones to the various horizons is shown. The assemblages of organic fossils most characteristic of these stratigraphic units (including the zone index species) are listed.