青藏高原东部第四纪冰川问题

本文讨论青藏高原东部地区第四纪古冰川遗迹,根据野外实地调查结合卫星影象和航空照片资料,说明末次冰期及倒数第二次冰期中古冰川从未联成M.Kuhle 等所称的大冰盖。各种证据说明,倒数第二次冰期降温最大,冰川、冰缘及河流加积作用明显,相当于深海氧同位素阶段6。在此之前有过漫长的大间冰期,致使倒数第三次冰期冰碛被侵蚀凌夷,表面发育红色风化壳。

THE PROBLEMS OF QUATERNARY GLACIATION IN THE EASTERN PART OF QINGHAI-XIZANG PLATEAU

Neither the continuous ice sheet suggested by M.Kuhle in Qinghai-Xizang Plateau,norsuccessive ice sheet of 400000km2 suggested by F.K.Ward was formed in the eastern part ofthe plateau.Our research indicates that in the ice ages of Quaternary period network moun-tain glaciers up to 200km long appeared in the marginal mountains of the plateau like ChayuValley and the glacier in Bomi region was up to 100km long.However,many valleys of largerivers,such as Jinshajiang River,Lancangjiang River,Nujiang River and Yalongjiang Riverwere never sculptured by the former glaciers.These areas were different from Karakoram-shan Mountains standing in the western part of the plateau,where the main valley of the In-dus was occupied by glaciers in the ice ages.In the headwater areas of the Changjiang Riverand the Huanghe River and some places where planation surfaces had been preserved in theinterfluves between big rivers like Shalulishan Mountain,ancient ice cap of several thousandkm2 grew,leaving over a large number of glaciated lakes,drumlins,roches moutonnees andso on.Many lakes and streamline bedrock landforms in the headwater area of the HuangheRiver between A'nyêmaqênshan Mountain and Bayankarashan Mountain seem to show that alocal ice sheet with an area of more than 50000 km2 might have developed,and the glacialmeltwater of the ice sheet was drained into Roergai and Gonghe basins.The former glacial relics in the eastern part of the Qinghai-Xizang Plateau can be di-vided into three groups representing three ice ages respectively.Their scales decrease gradual-ly from old to new.The glacial relics of penultimate ice age of them is still clear.In the up-per reaches of Dahebahe River,a （?）ranch of Huanghe River in Qinghai Province,the end mo-raine of penultimate ice age gradually merged into outwash terrace,which was in turn coveredby paleosol S1,representing isotope stage 5 of late Pleistocene and the loess up to Holocene.Ithas been verified that the ice age when the end moraine deposited must correspond to deepsea isotope stage 6 or L2 of loess sequence of China.The climate of penultimate ice age wasso severe that not only the snowline was depressed about 300m lower than that of last glacia-tion,but also the periglacial relics descended even much lower.In terms of sand wedges nearXinghai County,the air temperature in penultimate ice age was 10℃ lower than that of today.Because of the strengthening of periglacial action over vast area,the rivers got more clasticmaterials,so penultimate ice age is a powerful aggradational period.The Longyang Canyonhad been cut down for 800—1000m within the last 100000 years by Huanghe River afterthis aggradational period in Gonghe basin.The third ice age from the last seems to corre-spond with isotope stage 16 of deep sea core or with stage L6 of loess sequence,and its till hadpassed the warm time of stage S5 and experienced chemical weathering intensely.