Discovery of Shigu Paleolake in the Lijiang area, north western Yunnan, China and its significance for the development of the modern Jinsha River valley

The authors found more than a dozen outcrops of typical Quaternary lacustrine deposits on both banks of the Jinsha River near the "First Bend of the Yangtze River", Shigu, Yunnan, which constitute the bases of terraces II, III and IV of the Jinsha River. The results of the thermoluminescent and U-series dating and magnetostratigraphic research show that the ages of the middle and upper parts of the lacustrine deposits range from 243.3 to 88.0 ka BP, being equivalent to late Middle Pleistocene to early Late Pleistocene, while the ages of the deposits of overlying terrace IV range from 88.0 to 80.9 ka BP. The grain size, geochemical and clay mineral analyses of the lacustrine deposits show that their sedimentary environment had a trend of changing from warm-humid to hot-humid. According to a study of the Pleistocene glaciation of the Yulong Snow Mountains, "Paleolake Shigu" was an ice-dammed paleolake formed by damming of the Jinsha River valley by moraines of the early Middle Pleistocene Yulong glaciation and later further damming by glaciofluvial deposits of the late Middle Pleistocene Lijiang glaciation at the western foot of the Yulong Snow Mountains. It opened and overflowed owing to erosion of the modern Jinsha River more than 88,000 years ago.