Palaeoenvironmental Conditions of the Upper Middle Pleistocene Warm Intervals in the Upper Volga Region, Northwestern Russia, Based on Palynological, Paleocarpological and Quantitative Geochronological Data.

The climatostratigraphic scale of the Upper Middle Pleistocene in the northwest of the East European Plain contains a number of controversial issues, one of which is the position of the Likhvin (Holstein) Interglacial and lesser warm (interstadial) climatic events. To approach this problem, we have studied two sections of Quaternary deposits, Bolshaya Kosha (a well-known and long-studied natural exposure) and Nazarovo (a new, previously unknown section studied in a borehole), in which warm intervals of the Middle Pleistocene are recognized. In both sections, we performed lithological and paleobiological (carpological, spore-pollen) analyses and luminescence dating. In the Bolshaya Kosha section, seeds of the extinct species Caulinia goretskyi were revealed, which allowed us to attribute the obtained IRSL (ca 250–260 ka) dates to the post-Likhvin Bolshaya Kosha interstadial. The sum of data let us propose that both our IRSL and recently published ²³⁰Th/U dates (ca 240–290 ka) underestimate the age by 10–15%, and the post-Likhvin Kosha interstadial deposits were formed in the late MIS 9. In the Nazarovo section, palynological study showed the conditions of a relatively warm interstadial, with a change in the composition of vegetation from northern to middle taiga forests. According to IRSL dating, the section was formed in the MIS 10 late glacial between 330–370 ka. The two studied interstadials bracket the Likhvin (Holstein) Interglacial and sedimentary units in the Bolshaya Kosha section are proposed to have formed in MIS 9e. [ABSTRACT FROM AUTHOR]