The Stady On Change Of Paleoclimatic Environment In Early-Middle Holocene Revealed By Borehole QG01 In The Western Coast Of Bohai Bay,china

The borehole named QG01, drilled in northern west coast of Bohai Bay, 10-17.4m depth, is employed here for analyzing sediment environment and climatic evolution from late Pleistocene to the middle Holocene. On the basis of grain size characteristics, clay mineral characteristics, lithology characteristics and OSL dating method, compared with previous work in study area, some conclusions were drawn as follows:1. The deposition rate of the borehole named QG01 changes periodically which have good corresponding to rivers supplyment and sea level change. The first stage of the deposition rate is very low, controlled by terrestrial rivers from18 to 8.5ka BP. The second stage of the deposition rate is quite high, controlled by rising sea levels and progradation of rivers from 8.5 to 5.4 ka BP. The third stage of the deposition rate increase further under the influence of river supply from 5.4ka BP to now.2. The study area has undergone a significant change process from land to sea since late Pleistocene. It transited from flood plain facies and tidal flat facies to delta facies. The evolution of the sedimentary environment was controlled by rivers supplyment and sea level change in the study area since the Holocene. It was mainly controlled by sea level early, while by river progradation middle-late, especially the Yellow River delta’s influence on coastal change.3. Clay mineral combination is illite-chlorite-kaolinite-smectite in study area. The characteristics of the variation in content of the four kinds of clay mineral and the KI of illite shows there were some material came from the Yellow River in the study area during 7.2-5.6 ka BP.4. The ratio of(I+C)/(K+S) can be used as an index of ancient climate evolution, which indicate the cold and warm period of ancient climate compared with the KI of illite. Analysising the index of ancient climate evolution by the Mann- Kendall test, it is concluded that: the study area has experienced a process of gradual warming at the end of the last glacial maximum to the early Holocene, and the most significant of warming stage was 14-8.5 ka BP. In the early-middle Holocene, temperature rose slowly, including a less obvious cooling event during 8.3-7.9 ka BP, but it did not change the general warming trend.