New Radiocarbon and Paleobotanic Data on the Development of Glacial Lakes in Chukotka

摘要

Glaciers formed in the Late Pleistocene in the Pekul'nei Ridge (174°45′E, 64°55′-67°30′N) advanced toward the Anadyr Lowland leaving behind relatively large moraines as elongated arcuate terminal ramparts with a height of 60 to 103 m. These moraines, flu-vioglacial sediments, and eskers are coeval with the Tyellakh Group that characterizes the second half of the Late Pleistocene and includes the Zyryanka, Kar-gino, and Sartan intervals. The interfluve zone of lower courses of the Anadyr River and its left tributary (the Tanyrer River) located between terminal arcuate moraines is characterized largely by even or hummocky landscapes populated by sedge-gramineous communities with Rumex chamaemorus, Empetrum nigrum, Vaccinium uliginosum, and Rumex sp., as well as the low fruticose forms Betula exilis and Salix sp. The slopes and flattened surfaces of moraines are covered with shrubs (up to 1 m high): Pinus pumila, Duschekia fruticosa with Betula middendorffii, and Salix sp. The numerous lakes that developed within the moraine complex are often very large (2-6 km across) but shallow (1.5-2.0 m or less). The fall in the lake levels has resulted in the replacement of most of the large lakes by some isolated smaller basins, e.g., Lake Sanset located near the northern central slope of the moraine rampart (25 km long and 1.5-2.0 km wide), which is the largest one in the Anadyr-Tanyurer river interfluve. The southward-convex moraine (Kholmy Priozernye) joins another moraine rampart (Kholmy Zaozernye) in the east. Lake Sanset (altitude 36 m) was formerly a common basin 2200 x 1200 m in size.