Литосфера (Apr 2018)
Сonodonts from the boundary Artinskian-Kungurian deposits of Mechetlino section (Bashkortostan, the Southern Urals) Article I. Characteristic of the conodont associations
Abstract
The description of the section of Artinskian-Kungurian boundary deposits on Yuryuzan River right coast near the village Mechetlino is given. The low systematic diversity and vare low frequency of conodonts in the Artinskian-Kungurian interval in the Uralian sections are noted, which is an order of magnitude inferior to the representativeness of conodonts in the Asselian and Sakmarian Stages. Nine informative levels with conodonts in the ten-meter section, revealed by Mechetlino quarry, give the possibility to trace the stratigraphic distribution of the species from the sweetognatid and neostreptognathodid chronoclines and to find out morphological trends in the development of these groups of conodonts. The basic morphotypes of conodonts are described. The phylogenetic tendencies in the evolutionary development of the representatives of genera Sweethognathus and Neostreptognathodus are shown, on the basis of which is built the zone conodont scale for this stratigraphic interval and the lower boundary of Kungurian stage at the level of the appearance of the species Neostreptognathodus pnevi Kozur et Movschovitsch is established. The distribution of the conodont’ complexes in the section is shown, the dynamics and charakteristics of its change with time are analyzed. The Sarginskian horizon of Artinskian stage is identified well on the appearance of conodonts of the species-cosmopolite Neostreptognathodus pequopensis Behnken. This species loses teeth on the anterior part of the parapets and passes in N. pnevi Kozur et Movschovitsch. The species N. ruzhencevi Kozur appear together with N. pequopensis Behnken. N. ruzhencevi Kozur undergo in the Kungurian century the analogous metamorphosis, which led to the reduction of carinal tooth-edges on the anterior parts of the parapets. Such forms are isolated in the independent species N. lectulus Chern. The level of the appearance of the species N. pnevi and N. lectulus coincides with lower boundary of Kungurian stage.
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