Литосфера (Jun 2018)
Сonodonts from the boundary Artinskian-Kungurian deposits of Mechetlino section (Bashkortostan, the South Urals). Article II. Stratigrafic distribution of conodonts
Abstract
The images of the species of conodonts from the section of boundary Artinskian-Kungurian deposits on by right to coast Yuryuzan River near the village Mechetlino are given and commented. The stratigraphic distribution of species in the section is shown, their changes are analyzed. Text is accompanied by ten tables with the images of conodonts. The forms from the upper part of Artinskian (Sarginskian horizon) of the section depicts in the table I. These species of conodonts Neostreptognathodus ruzhencevi Kozur and N. pequopensis Behnken are meeting the most frequently in the Sarginskian horizon. Quantity of pairs of nodules in the Sarginskian representatives of the species N. pequopensis Behnken rarely exceed 4-6, moreover the posterior pair of nodules frequently grows together. The species Sweetognathus somniculosus Chern. is found in the Sarginskian horizon too. The morphology of the specimens of this species varies from the morphotypes, which possess almost one-piece carina, hardly by noticeable narrowings at the posterior end, to the forms with the distinctly differentiated posterior end of carina. Conodonts, depicted in the Table II, occur from the bad 9, in upper part of which the forms N. pnevi Kozur et Movschovitsch and N. lectulus Chern. are found. These species are the indicators of lower boundary of Kungurian stage. Forms in the Table III of the bed 10 and majorities of the depicted forms relate to the species N. lectulus Chern. The species N. labialis Chern. with narrow platform, incomplete developed middle groove and with the outlined narrowing in the posterior part of the platform here for the first time appears. The typical N. ruzhencevi Kozur continue to be encountered in the bed 10. Forms on the Tables IV-VII relate to the most representative complex of conodonts from the upper part of the bed 12, where more than 60 the specimens of conodonts found. The large part of the specimens, placed in the Table IV, relates to the phyletic sequence of forms from Sweetognathus somniculosus Chern. to N. labialis Chern. The forms, which relate to the species Neostreptognathodus pnevi Kozur et Movschovitsch, N. lectulus Chern., N. pequopensis Behnken in the Tables V, VI are represented. The members of phyletic line Neostreptognathodus pseudoclinei Kozur et Movschovitsch - N. labialis Chern. presents in the Table VII. The composition of conodonts in the subsequent informative beds 13, 14, 16 of the Saraninskian horizon remains. Conodonts of the Philippovskian horizon found west of quarry Mechetlino. They are represented in the Table X: Neostreptognathodus aff. clinei Behnken, N. clinei Behnken, Sweetognathus nov. sp. 2 , Uralognathus cochleatus Chern. Section Mechetlino is recommended as limitotype of lower boundary (GSSP) of the Kungurian stage of the International stratigraphic scale.
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