New species of small foraminifers from the Mechetlino Quarry section (Southern Urals, Russia): a potential candidate for the GSSP of the lower boundary of the Global Kungurian Stage

Four new species of small foraminifers, Hemigordius infantem sp. nov., Pseudoammodiscus valeryi sp. nov., Nodosaria septumlamellosa sp. nov., and N. zebra sp. nov., are described from strata near the Artinskian/Kungurian boundary in sections of the Southern Urals (Mechetlino Quarry), Middle Urals (Kamayskiy Log), Preuralian Foredeep, and the Sol-Iletsk Swell (boreholes of the Nagumanovskaya Field), Russia. High morphological variability of Hemigordius infantem sp. nov. is noted. It is shown that lateral thickenings and wall structure may not be preserved as a result of subsequent lithification processes. The lumen shape of the last whorl and test morphology are more constant features for all specimens of Hemigordius infantem sp. nov. The high variability of dimensions of H. infantem sp. nov. and Pseudoammodiscus valeryi sp. nov. is clearly seen in the binary discriminative diagrams of the dependence of some features of the tests depending on the number of whorls (test size and proloculus diameter). For the first time, the appearance of species of Nodosaria with a multilayered, poly- or plesiomonolamellar wall have been noted in the upper Artinskian deposits in the Urals. Such a wall is known only in Artinskian and Kungurian deposits in the Urals, and in Artinskian, Kungurian, and Kazanian deposits of the north and northeast of Russia. The appearance of this feature may be a good marker of the upper Artinskian (upper part of the Sarginian), Neostreptognathodus pequopensis Conodont Zone, near Artinskian/Kungurian boundary.