Middle Pleistocene Warming Phase Based on the Deposits of a Buried Oyster Reef, Southern Lesser Kuril Islands

摘要

Information about manifestation of a wanning phase in geological history is of great interest from the viewpoint of estimating the tendencies of environmental evolution under climate changes of recent decades. The Middle Pleistocene climate rhythmicity in the southern Russian Far East has been studied studied fragmentarily. However, the Pleistocene is characterized by a series of remarkable warmings, whose variations, intensity, and time spans need to be investigated. Middle Pleistocene paleoclimatic reconstructions have been made for Primorye, Sakhalin, and Chukotka. For the Kuril Islands, the deposits of this age have been studied poorly and the results obtained are quite ambiguous. This is related to poor preservation of the sedimentary covers in small island territories due to erosion during the subsequent transgressions, high dynamicity of the islands, intensive volcanism, and other factors. The main objects of paleoreconstructions are the deposits of coastal swamped lowlands; these deposits are characterized by frequent facies changes and poor preservation. Strati-graphically sound constructions of the Middle Pleistocene have been made for the Greater Kuril Islands, where deposits of two transgressions (MIS-11 and MIS-9) were distinguished on Kunashir Island; on Iturup Island, the Middle Pleistocene is represented by a 25- to 30-m terrace.