Palynological Characteristics and Volcanic Ash from Sediments of Chistoye Lake, Northern Priokhotye

Abstract

Chistoye Lake (59° 32' N, 151° 48' E) is located 10 km from the northern coast of Taui Bay (Okhotsk Sea) in the central part of a tectonic depression that has been infilled with Paleogene and Neogene deposits. The lake originated as the result of glacial activity during the latest Pleistocene (MIS2). A 550-cm-long lacustrine sediment core was raised from Chistoye Lake using a piston sampler. The core is dominated by silt with layers of peat and sand at its base. The silt includes two tephra layers at 360-364 cm and 77-80 cm. The tephra layers have different geochemical, magnetic, and mineralogical properties. Volcanic ash like the lower tephra in the Chistoye core has been found in other lacustrine sites from the Upper Kolyma, Upper Indigirka, and Northern Priokhotye regions. Radiocarbon dating of organic remains that bracket this second tephra, corresponding to the lower tephra in Chistoye Lake, indicates an age of 7 650 ± 50 years ago, which is comparable with the age of the Kurile Lake - Iliyinskaya caldera forming eruption in Kamchatka. The younger tephra also has been noted in cores from other lakes in Northern Priokhotye and dated to 2 745 ± 10 years ago. A distinctive feature of this Late Holocene tephra is its high magnetic susceptibility. Extrapolation of a sedimentation rate based on the tephra ages suggests that the Chistoye record is approximately 11 700 years old. Palynological analysis of the Chistoye Lake material showed that all samples contain pollen redeposited from Neogene sediments (Picea sect. Eupicea, Tsuga, Tilia, Corylus, Juglans, Ulmus). These taxa can be easily discounted as contaminant, but other pollen types (e. g., Pinus subgen. Haploxylon, Betula, Alnus, Cyperaceae, Poaceae) are more problematic for interpreting the paleovegetation, because they represent plants that were present during the Holocene and/or the Late Pleistocene and during the Neogene. Nonetheless, the changes in the percentages of Sphagnum spores suggest a gradual increase in effective moisture during the Younger Dryas and Holocene. A multiproxy study of the sediments from Chistoye Lake, in conjunction with their palynological characteristics, shows the importance of analyzing magnetic properties to help determine the presence of tephra in the sediments. Volcanic ash layers in the lake sediments from northeastern Siberia are reliable chronostratigraphic markers that can supplement radiocarbon dates and improve the regional understanding of climate and vegetation changes during the Holocene.