Organic geochemical proxies (δC13 and C/N) are used to infer changes of plant fossils sources in the sediments of relict mire lakes in Russia. The Pleistocene Holocene transition is described by δC13 and C/N used jointly. Shifts of C/N and δC13 give ideas for the lakes water level and composition of plant remains changes as a consequence of the regional climate alterations. Pre-Holocene cool period (Younger Drias) and preceding warm phase (Allerød) are supposedly traced in the lake sediments for the north of the Mologa-Sheksna Lowland.