关键词: 青藏高原, 临夏盆地, 古气候演变, 30MaB.P.

Abstract: The Cenozoic sediment in Linxia Basin, which locates at the northeastern fringe of Tibet plateau bears abundant informations on the plateau's uplift and paleoclimate. The paleoclimatic sequence revealed by geochemical elements (oxides) since about 30MaB.P. basically coincides with that revealed by spore-pollen combinations, i.e., during most of the Teritary, although climate alternated by warm-moist and cold-dry, it generally represented a relative stable regiem. After stepping into the Pliocene, climatic unstablity increased clearly, alternated drastically and frequently by the periodes of cold-dry and warm-moist. Untill in the early Quaternary, a cold-wet regiem appeared. This process perhaps reflects to a certain degree a dynamic process which the Asia monsoon displayed unobviously before the pliocene, began to establish in Pliocene, and established in the early Quaternary. Fluctuatins of geochemical contents are of profound tectonic-climatic background, the periods in which geochemical contents fluctuated violently correspond to the active tectonic periods, and the climate turned to be cold. Spectrum analyses of the high resolution CaCO₃ curve show that during 30 Ma～1-67 Ma, climate was mainly controlled by 21ka and 41ka cycles; but during 1-67 Ma～0-73 Ma, the quasi～100 ka cycle appeared, and got more and more obvious; till after 0.73MaB.P., the 100 ka cycle became predominant. The loess record in our country has also revealed the similar result, and showed that the climate was modified greatly since the Tertiary, which maybe closely related to the pulsating uplifts of the Tibet plateau.

Key words: Tibet plateau, Linxia basin, paleoclimatic change, 30MaB.P.