昆仑山垭口地区的冰期系列

Glaciation Sequences in the Kunlunshan Pass Area

通过对昆仑山垭口地区冰碛和其它沉积物的物的野外调查及室内分析，并在运用各种年代学手段测定沉积物绝对年代的基础上，建立了垭口地区第四纪以来的冰期系列．即望昆冰期、垭门冰期、玉珠峰冰期、晚冰期、新冰期和小冰期．本区迄今未发现早更新世冰斯．

The Kunlunshan Pass is located in theTibetan Plateau, between the Qiangtang Plateau andthe Qaidam Basin. Landform and sedimentary evidence shows that glaciations had occurred in theQuaternary.The moraines of the earliest and greatestglaciation in this region are found on the ridges of theKunlunshan beside the Jingxiangu valley and on thehill top of the southwestern Kunlunshan Pass.Tectonically tilted till is found on bedrock, alluvialfan sediment of Jingxiangu Formation, lacustrine andfan--delta sediment of Qiangtang Formation. The tillis named Wangkun Till and this glaciation is namedWangkun Glaciation. According to paleomagneticdating, the B / M boundary has been found at the upper part of the Qiangtang Formation(near the top ),with an age of 0.73 Ma BP. The TL age of theWangkun Till is 543.47±109.69 ha BP, and ESR ageis 710± 228 ha BP. So the conclusion is that theWangkun Glaciation occurred from 0.7 Ma BP to 0.5Ma BP. The evidence of earlier till is found on thesouth slope of the eastern Kunlun Mountains andaeolian sand sediment is found in the lower part ofSanchahe Formation. This earlier glaciation is namedYakou Glaciation, and is dated about 0.26 Ma BP.The till of early Period of the Last Glaciation has beendestroyed, however aeolian sand remains in the upperpart of the Sanchahe Formation provide an evidenceof cold environment, with an age about 60 ka BP. Theclimax of the Last Glaciation exhibits one moraine,which is called Yuzhufeng Glaciation, formed in 20 to18 ka BP. Only one moraine is found of the LateGlaciation, formed in 14 to 13 ka BP. The morainesof Neoglaciation and Little Ice Age remain at the endof the modern glacier. The Neoglaciation tills formthree discontinuous moratines, about 5 m in height.The distance between the morain and the end of themodern glacier is about 80~100 m. The moraine ofthe Little Ice Age is located on mountain slope, andthere is an evident difference between theNeoglaciation and the Little Ice Age till.A detailed study reveals that the JingxianGlaciation and the Nachitai Glaciation, which werenamed by the former researchers, never existed. Theso-called“Jinxian Till” is actually the Wangkun Till.It was impossible to develop glacier during theTertiary and the early Pleistocene Period, because theelevation of this area was only about 1 000 m a.s.l. atthat time. The diamicton of Nachitaigou Formationhad been regarded as till, however there aregeomorphological and sedimentary analyses suggesting that it is debris-flow sediment.Based on the above facts, there are followingglaciations in this area: Wangkun Glaciation,YakouGlaciation, Yuzhufeng Glaciation, Late Glaciation,Neoglaciation and Little Ice Age. According to the tilldistribution it is believed that the scope of theglaciations decreases with time.