THE CHANGES OF DALAINOR LAKE
Guo Zhaoshan(The 3rd Geolog cal Team of the Geological Minerals Bureau, Nei-Menggu Antonmous Region)
The studied region is situted at the westernbor der of Chifeng city, with its south western part bordering the city. Its location is about 116°26/-117°15'E and 43°30'-42°40/N, in the northwest of the region, The surface of the lake approximates 1226m a.s.1.. with an east-west width of 15 km and a length of 21km, covering an area of 225km2. The depth of it is geverally 10m, and the deepest place 13m. Dalainuoer (Dalainor) is located in the most developed part of the compossion rift belt of Xilamuleng River at the old lake region. Its is a structural lake. At the beginning of Tertiary period it was a part of the lake sea ia Nei-Menggu (Inner-Mongol) Plateau At the middle Pleistocene, the Jake was formed near Haoluku, with an area about 8% of the whole region, and at the end of Middle Pleistocene, it enlarged to half of the (river source) basin. At Middle late Pleistocene the lake covered a large part at both sides the of present divide at the end of Plei-socene, it overflowed across the present divide to the whole region and even beyond the studied region. That was the most flourishing period of the lake. At Holocene earthcrust consistently uplifted, while the lake shrank to the present depression situated west of the divide and north of Daerhan There are five rivers such as Kang alkula Piiver and others flowing into the lake, forming a centripetal inland drainage.At the beginning and late periods of Middle and late Pleistocene, the earthcrust of the region relatively uplifted, which caused the lake water to dissipate, mainly to dry up. From early Pleistocene to Holocene, the lake water appeared four times and disappeared four times. Thus the lacustrine and fluvial deposits left in the region have a thickness of 15C-200m rich in ground water resources.