Vol 27, No 6 (2019)

In the present paper we describe and discuss belemnite finds from the basal part of the middle Jurassic sequence at the southwest of the Republic of Tatarstan (Tetyushi district). The belemnites were collected from the outcrops located along a shoreline of the Kuybyshevskoye reservoir (Volga river) between the place Tarkhanovskaya pristan’ and the former village Dolinovka. These belemnites indicate that the basal part of the Jurassic sequence is Early Bathonian (Ishmae Zone) or, less probable, Middle Bathonian in age. Such dating triggers a critical review for the age of the middle Jurassic sequence in the region. In particular, poorly preserved ammonites previously collected from the same outcrops higher in the succession and interpreted as members of the Late Bajocian subfamily Garantianinae, are in fact Late Bathonian Gowericeratinae. Consequently, “Beds with Garantiana”—nominally the most ancient ammonite-based biostratigraphic unit within the whole Jurassic of European Russia, based on this assemblage,—is invalid.

The results of palynological and micropaleontological studies of the Upper Cretaceous–Cenozoic strata penetrated by Boreholes 23 and 19 of the Aleiskaya area (Altai krai) are presented. The obtained data allowed us to substantiate the age of the deposits, make suggestions concerning their depositional environment, and to clarify the subdivision of geological section into formations. Two palynological assemblages were recognized in the Cretaceous part of the Borehole 23 section: the first one characterizes the Len’ki Formation and is dated as Cenomanian–Turonian; the second one is recognized in the Upper Sym Subformation and is dated as Maastrichtian. The Upper Cretaceous sequence is overlain by the terrestrial Ostrovnoe Formation (Paleogene). In Boreholes 19 and 23, this formation contains presumably Late Paleocene–Early Eocene and Middle Eocene spore and pollen spectra, respectively. Palynological data substantiate the Late Miocene age of sedimentary strata in the upper part of the geological section of Borehole 23 and their belonging to the Pavlodar Formation. The structure of the palynological assemblages, the specific features of the macerate, and the absence of foraminifers indicate the continental genesis of the Upper Cretaceous–Paleogene sedimentary deposits in the southern part of the Kulunda Depression in Altai krai.

For the first time, sections of the Upper Miocene Ishim Formation in the south of Tyumen oblast near the villages of Pyatkovo, Masali and Bigila were thoroughly studied by the palynological method. A series of mineralogical analyses of these sediments and radiocarbon analysis of the Quaternary sediments overlying the Ishim Formation were carried out. Four palynological assemblages (PA) were established in the Ishim Formation: PA1 with Botryococcus; PA2 with Botryococcus and Sigmopollis; PA3 with Alnus, Polypodiaceae, Botryococcus, and Sigmopollis; PA4 with Betula, Alnus, and Corylus. The layers with PA1, PA2, and PA3 were observed in two sections near Masali and Bigila. PA4 was found in sands and aleuropelites in the outcrop near Pyatkovo; it contained a significant amount of diverse pollen of temperate thermophylic broad-leaved taxa and scarce elements typical of Miocene (Taxodiaceae, Nyssa, and Tsuga). PA3 and PA4 were compared to the known complexes of Neogene sediments in Western Siberia. PA5 with Betula, Herbae, and Fungi was discovered in the bedded silts overlying the Ishim Formation in Masali outcrop. Previously, these sediments were attributed to the Late Miocene Pavlodar Formation. The composition and the structure of PA5 suggested Quaternary age of the hosting sediments. Radiocarbon analysis of the organic substance occurring in the silts has shown that these sediments were accumulated in the Late Pleistocene (Sartan Ice Age). For the first time, the information about microphytoplankton (Botryococcus, Pediastrum, Zygnemataceae, Sigmopollis) and other non-pollen palynomorphs contained in the Ishim Formation (Upper Miocene) and in Pleistocene sediments is presented. Development stages of the Late Miocene Ishim Basin were distinguished, the vegetation surrounding this basin was described, and the depositional environment of Pleistocene sediments (Masali outcrop) was reconstructed using palynological data.