Characteristic Of Palynofloras And Climatic Change During Holocene In The Cuoqin Area Of The Tibet

As a cross-section and the latest chapter of geology history, the climatic change of Holocene play an important role as the connecting link bewteen the preceding and the following research of global change. The record of palaeovegetation changes is one of the best method to recognise the global, regional and local changes. Which not only can be able to indirectly check the climatic patterns, but also can be able to know the stability and sensitive degree of environmental elements. The climatic changes attract the Chinese and foreign scientists attention recently, especially the effect to summer monsoon wind of Asia because of the plateau uplift during Holocene in the Qinghai-Tibet Plateau. Studies on Holocene climatic changes in the plateau hinterland is one of key factors to solve the problem. However, the problem can not be solved perfectly in time scale or space on the basis of the existing research data. The argillaceous sediment section which contents carbon are choosed to spore-pollen studies and palaeoclimate reconstruction in the Cuoqin area of the hinterland of plateau.After geological field work, a topical section are chosen to study in Cuoqin area. We collected 51 samples for spore-pollen analysis at the interval of 10cm and 2 samples for AMS¹⁴C dating. Based on the result of pollen analysis, we construct spectrums of the quality concentrations and the percentage respectively, and then discuss the vegetation types and the climatic evolvement. It can be concluded as follows:(1)Based on the variations of the Pollen concentration and assemblages, four pollen assemblage zones in Cuoqin section were identified from the bottom to the top.(2)The palaeovegetation, palaeoclimate were reconstructed based on pollen assemblages and described in ascending order as follows: The main botanic types were high mountain steppes or bushwood meadow steppes with arid and cold climate from 10500 to 9370aBP. It was a transition stage from meadow steppe to steppe vegetation, indicating semiarid and cool climate during the period of 9370—7490aBP. The climate and environment were better than the second stage, and to forest shrub steppe with a small dry and a temperate climate in the period of 7490—5200aBP. During the periods of 5200—3010aBP, the vegetation composition changed after the formal stage. The steppe was dominated by high mountain steppe with Cyperraceae, Artemisia. It tended to be semiarid and cool.(3)Compared with studies of nearby areas, the climatic changes recorded in spore-pollen in Cuoqin area are basically in accordance with them. Climatic change sequence are as follows: algid stage, heating-up stage, miothermic stag, cool stag.(4) According to spore-pollen analysis, Holocene Thermal Maximum is identified in this area, which prove that the climatic change process during Holocene in the hinterland of plateau is in accordance with global climate.(5) 9300aBP dry-cold event found in the northern hemisphere is firstly identified. The event is at the same time with that recorded in Guliya ice core locate at Kunlun mountain in north edge of Qinghai-Tibet Plateau as well as in inland and pelagic. Which shows that this event recorded in the hinterland of plateau happened all over the world.