Nadezhda Alexeeva

Pliocene and Pleistocene biostratigraphic succession of Transbaikalia with emphasis on small mammals

This paper deals with the Pliocene, Pleistocene and Holocene mammalian faunas of the Transbaikal area for which 15 successive mammalian faunas are recognized. This review is based on the study of new paleontological materials obtained from several Late Cenozoic localities and reexamination of existing faunal data. Stratigraphically, the oldest fauna is known as Udunginian. It contains mostly fossils of forest inhabitants and few arvicolids. This fauna was replaced by the next Pliocene hipparion assemblage known as the Chikoi Faunistic Complex, characterized by the dominance of forest-steppe and open landscape inhabitants, as well as by the abundance and diversity of rooted arvicolids. The Itantsinian Complex is the following faunistic level of the Late Pliocene. It is characterized by the first appearance of Equus and Spermophilus and by the presence of progressive taxa of rooted voles. The Early Pleistocene fauna is characterized by the appearance and abundance of rootless arvicolids and by the continued existence of the latest rooted voles. The Middle Pleistocene Tologoi Faunistic Complex is distinguished from the preceding one by the disappearance of rooted voles. The Late Pleistocene fauna featured a diversity of Microtus taxa and an abundance of Lasiopodomys and Ochotona species. The majority of the Late Pleistocene small mammals belong to recent species, although some of them were distributed over a greater area at that time than at present.

Geology and fauna, and preliminary correlation of sediments of the main Late Cenozoic sites of the Transbaikal area

Abstract The Pliocene and Pleistocene sediments exposed in eight sections of Transbaikalia have been correlated using geological and palynological data, together with information on fossil mammals and some paleomagnetic characteristics. The most complete sequence of fossiliferous deposits (spanning the time interval from the Middle Pliocene to the Late Pleistocene) is exposed in the Tologoi key section. The sequence was correlated with other sections primarily on the basis of mammal faunas. During deposition of the Chikoi Suite, Udunginian, Chikoian and Itantsinian faunal complexes appeared in succession. Four successive stages in mammal evolution are recognized within the Early Pleistocene. Deposition of the Krivoyarskaya Suite proceeded throughout the time when the Tologoi faunistic complex, Ivolginian and other Pleistocene faunas followed each other in the Transbaikalian region.