The mid-Moscovian Izvarino section, Donets Basin, eastern Ukraine, exhibits a complete sedimentological record of siliciclastics (sandstones, siltstones, and calcareous shales) with limestone intercalations and, rarely, coal seams. A multidisciplinary study including microfacies analysis, systematic paleontology (conodonts, fusulinoideans, and ostracodes), biostratigraphy, and paleoecology was focused on the limestones, from limestone L4 through limestone M1, and the adjacent marine shales. Based on sedimentology and fossil associations, the cyclic sediments of the Izvarino section were interpreted as entirely marine deposits of open- and shallow-marine, nearshore and offshore environments with variable terrigenous input.
The well-preserved ostracode faunas are dominated by representatives of the families Amphissitidae, Hollinellidae, Healdiidae, Cavellinidae, and Paraparchitidae. The total fauna is 18 species, of which four are new: Hollinella (Hollinella) granuloba Fohrer, n. sp., Hollinella (Praehollinella) kamenka Fohrer, n. sp., Jordanites krasnodonensis Fohrer, n. sp., and Asturiella donbassica Fohrer, n. sp. The conodont fauna includes 21 species belonging to nine genera and includes one new species: Idiognathodus izvaricus Nemyrovska, n. sp. The conodont faunas are dominated by idiognathodontids. Representatives of Diplognathodus and Neognathodus play a subordinate role. A total of 56 fusulinoidean species referable to 20 genera has been identified; one is new: Eostaffella brazhnikovae Ueno, n. sp.
Conodont and fusulinoidean biostratigraphy led to surprising differences in the age assignment of the Izvarino section and its correlation with the nearby Moscow Basin, Russia. The interval studied is lower Kashirian (Tsninskaya) to middle Kashirian (Narskaya), according to conodonts. It extends to the base of the Podolskian, however, according to fusulinoideans. This discrepancy is possibly related to problems in correlation of the type sections in the Moscow Basin. It calls for reexamination of the mid-Moscovian boundary interval and shows the limits of interbasinal correlations based on a single fossil group.
