THE CENOZOIC GEORECORDS IN THE NORTHWEST OF YUNNAN AND THE EVOLUTION OF QING—ZANG PLATEAU

The Cenozoic strata are well developed in the northwest of Yunnan Province, where the eastern boundary of Qing—Zang (Qinghai—Xizang) plateau is located. The rich geo\|records in the Cenozoic strata can help us to recapitulate the evolution history of Qing—Zang plateau.1\ The Cenozoic Strata Ninglang Formation (Paleocene—Middle Eocene) is composed of massively bedded conglomerate , mudstone in the lower part, purple thinly bedded—medium bedded fine quartz sandstone and sandy shale in the upper part, 600m thick. Lijiang Formation (Upper Eocene) and Jinsichang Formation (Oligocene): conglomerate, with a little sandstone in lower part, claystone, with a little conglomerate in the upper part. Lijiang Formation unconformably overlies on Ninglang Formation or even older strata, 1500～2000m thick. Shuanghe Formation (Miocene): thinly—massively bedded muddy siltstone, fine sandstone, marl, with several layers of coal. It unconformably overlies on Jinsichang Formation or even older strata, 108m thick. Sanying Formation (Pliocene): Claystone, siltstone, with a little lignite in the middle and upper part, conglomerate at the base, 110m thick, widely spread in the northwest of Yunnan.Sheshan Formation (early Pleistocene): pebbles, sands and clay layers. It unconformably overlies on the older strata, 100～187m thick.Heyunsi Formation (middle Pleistocene): poorly sorted and poorly rounded gravel and sands, 100～347m thick.Upper Pleistocene Series: glaciers—gravel, sands and clays; alluvial—sandy gravel layer(terraces); lacustrine—fine sand, silt and clay layer, 100 m thick.Holocene Series: lacustrine—sand, silt and clay layers; alluvial—sandy gravel layer (terraces), 50m thick.