Middle-Upper Quaternary stratigraphy in the northeast of European Russia inferred from rodent record and lithology of tills

摘要

We present the revision of materials on Quaternary rodent biostratigraphy (collared lemming Dicrostonyx and narrow-headed vole Lasiopodomys gregalis) in the northeast of European Russia testing the biostratigraphic method with lithological and palynological data. Petrographic composition of clastic material and orientation of clasts in fills are regionally stable lithostratigraphic criteria. Pechora (Dnieper) moraine is characteristic for clast axes oriented in the sector 340-60 degrees; clasts in Vychegda (Moscow) fill show orientation of 270-360 degrees, which, in combination with the petrographic composition of erratic material, indicates the origin of moraines from different source glacial provinces. Certain differences were also found in the associations of heavy minerals. A specific trait of the Upper Neopleistocene Polar fill is the presence of erratic crinoid-bryozoan limestones from Novaya Zemlya. Connection of this fill with the Pay-Khoy-Novaya-Zemlya ice center and, possibly, with the shelves of the Barents and Kara Seas is also confirmed by the orientation of clasts from north-northeast to south-southwest.Middle Neopleistocene rodent remains are found between the Pechora and Vychegda moraines. By the ratio of M1 and M2 morphotypes all Middle Neopliestocene assemblages are divided into three groups representing morphs: D. simplicior morph 2 (Gavrilovka, Bolshaya Sluda, Akis', Laya-4), D. simplicior morph 3 (Sercheyu-1, Laya-3) and D. ex gr. simplicior-gulielmi (Shapkina-4, Chuley, the lower horizon of Kipievo). These evolutionary levels respectively correspond to late Pechora (Dnieper, MIS 8), Rodionovo (Shklov, MIS 7) and early Vychegda (Moscow, MIS 6) intervals.Biochronological criteria for Late Quaternary based on evolutionary level of teeth of collared lemming and narrow-headed vole are suggested. It has been revealed that the early Valdai (MIS 5d-a-4) is characterized by the morph 2 D. gulielmi, as well as the high (about 50%) proportion of the gregaloid morphotype among the first lower molars of L. gregalis. Lemmings of morphs 2 and 3 D. gulielmi lived during the Middle Valdai (MIS 3), and animal of morphs 3 D. gulielmi and D. ex gr. gulielmitorquatus existed during the Last Glacial Maximum. Lemmings at the levels of D. gulielmi morph 3, D. ex gr. gulielmi-torquatus, D. torquatus morphs 1 and 2 were typical for Lateglacial; morphs 1 and 2 D. torquatus - for the early Holocene; morph 3 D. torquatus - for the late Holocene and recent times. Small (less than 25%) proportion of the gegaloid morphotype is characteristic of ml of Middle and Late Valdai and modern narrow-headed voles.