摘要
Shorelines are widespread and lake deposits and lake geomorphology are welldeveloped on the northern Tibetan Plateau. Through field observations of lacustrine deposits of NamCo-the highest and largest Quaternary lake in Tibet, the authors found four-step shore terracescomposed of sands and clays with well-developed horizontal bedding and 3-12 m, 15-22 m, 25-30 m and35-45 m higher than the lake surface respectively, lacustrine deposits resting on the bedrocks and60-150 m higher than the lake surface, and up to approx 50 levees composed of oblate lakeshoregravels. Moreover they found lacustrine and lakeshore deposits making up the terraces and levees onthe bottoms of wide dividing valleys connecting Nam Co with the Rencoyuema, Rencogongma and Jiuru Conorthwest of Nam Co (the valley bottoms are 20 m, 90 m and 60 m higher than the above-mentionedthree lakes) and on slopes north of it, i.e. terraces II and III of Nam Co. Thus they confirm thatNam Co and Ring Co-Jiuru Co had connected with each other several times, i.e. formed a unified largelake several times, rather than had been different lakes connected only by river channels. Fromindications such as the distribution of the highest shoreline and lake deposits and geomorphology,the authors conclude that the total area of the old large lakes on the northern Tibetan Plateau is afew times larger than that of the modern lakes and that the last-stage old large lakes formed inthe interglacial interval of the last glaciation.
Shorelines are widespread and lake deposits and lake geomorphology are welldeveloped on the northern Tibetan Plateau. Through field observations of lacustrine deposits of NamCo-the highest and largest Quaternary lake in Tibet, the authors found four-step shore terracescomposed of sands and clays with well-developed horizontal bedding and 3-12 m, 15-22 m, 25-30 m and35-45 m higher than the lake surface respectively, lacustrine deposits resting on the bedrocks and60-150 m higher than the lake surface, and up to approx 50 levees composed of oblate lakeshoregravels. Moreover they found lacustrine and lakeshore deposits making up the terraces and levees onthe bottoms of wide dividing valleys connecting Nam Co with the Rencoyuema, Rencogongma and Jiuru Conorthwest of Nam Co (the valley bottoms are 20 m, 90 m and 60 m higher than the above-mentionedthree lakes) and on slopes north of it, i.e. terraces II and III of Nam Co. Thus they confirm thatNam Co and Ring Co-Jiuru Co had connected with each other several times, i.e. formed a unified largelake several times, rather than had been different lakes connected only by river channels. Fromindications such as the distribution of the highest shoreline and lake deposits and geomorphology,the authors conclude that the total area of the old large lakes on the northern Tibetan Plateau is afew times larger than that of the modern lakes and that the last-stage old large lakes formed inthe interglacial interval of the last glaciation.
