倒数第二次间冰期以来黄河下游冲洪积物释光年代及其古气候意义

The alluvial sediments preserved in the loess along the lower reaches of the Yellow River documented the hydrological and climatic changes processes. Presently, the researches on the identification and hydrological reconstruction of alluvial events in the basins of the Yellow River mainly focus on the middle and upper reaches, while the studies on alluvial events in the lower reaches of the Yellow River are scare. Typical alluvial materials are generally preserved in the loess between the north Central Shandong Mountains and the south bank of the lower reaches of the Yellow River. The research region is located in the humid and semi-humid East Asian monsoon climate region with annual average precipitation is 700~900 mm concentrated from June to September. There are generally horizontal, spatially traceable, one or more obvious alluvium or diluvium preserved in the loess section. In this paper, four representative loess sections were investigated by luminescence dating, including Xiao Zhang Zhuang(36° 33'21″N, 118° 29'25″E; 4 luminescence samples were collected within the thickness of 635 cm), Zhi Dong Yu(36° 10'47″N, 116° 20'45″E; 2 luminescence samples were collected within the thickness of 450 cm), Jiu Long Yu(36° 33'20″N, 118° 29'17″E; 2 luminescence samples were collected within the thickness of 290 cm)and Tao Yu Cun(36° 08'16″N, 116° 19'39″E; 2 luminescence samples were collected within the thickness of 350 cm)sections. Gravels of these alluvial sediments with the thickness of 20~70 cm were mainly limestone with poor sorting, roundness and diameter less than 50 cm. Totally, 10 luminescence samples were collected to obtain the buried ages of the alluvial sediments.

Two samples(TYC-1 and TYC-2)of alluvial sediments were studied by using quartz single aliquot regenerative dose protocol(SAR)and the remaining 8 samples were measured by potassium K-feldspar infrared post infrared luminescence dating method(pIR200 IR290). The luminescence dating results were basically consistent with the field stratigraphic sequence. According to the sedimentary ages of the alluvial deposits, it can be divided as follows: interglacial periods(248~196 ka, 110~73 ka), transition periods between the glacial and interglacial periods(177~94 ka, 142~94 ka)and glacial period(26~18 ka), and indicating that precipitation variability increases during the interglacial time and transition periods, especially the time ranges from 110 ka to 94 ka. The results and information of climate changes recorded by various carriers in China are mutually evidenced, which further indicated that hydrological and climatic changes in the study area were a response to global environmental variations. This study supplements the chronological data of alluvial sediments in the lower reaches of the Yellow River, which is not only conducive to reveal the regional response mechanisms to global climatic changes and establish the possible relationships with global climate and environmental changes, but also provides reliable references for regional comprehensive development, management, ecological environment restoration and protection.