The accumulation records of environmental evolution on the salt-water intruded area south of Laizhou Bay since late Pleistocene
ZHANG Zu-lu 1, NIE Xiao-hong 1, LIU En-feng 2,3, XIN Liang-jie1 (1.Geography Department of Shandong Normal University, Jinan 250014, China; 2. Nanjing Institute of Geography & Limnology,CAS, Nanjing 210008, China; 3. Graduate School of the Chinese Academy of Sciences,Beijing 100039, China)
The south coastal plain of Laizhou Bay is one of the typical salt-water intruded areas, whose occurrence and development have a close relation with the environmental evolution since late Pleistocene. This paper deals mainly with the systematic palynological, microfossil, granularity research and 14C dating on more than 29 samples from a column core with a depth of 29m of core A1 for the purpose of revealing the characteristics of paleoenvironmental evolution since late Pleistocene.According to the systematic study, 7 phases of the paleo-climate fluctuations and paleo-vegetation successions since late Pleistocene are identified. And 7 climate periods can be listed in the ascending order for the convenience of correlation: ①120-85kaBP, the analysis of spores,pollens and sediments shows that the then climate evolved from cold into warm and a little dry gradually;②85～76kaBP,obvious manifold pteridophyte and exiguous granularity of sediments showed a local humid environment with swamps and lakes developed in the lower reaches of the Weihe River; ③76～50kaBP,equal to the secondary Ice Age of Dali, characterized by grassland vegetation type with conifer in domination, and coarse sediments showed a barren terrestrial environment;④50～24kaBP,cold,wet-resistant hydrophyte such as bulrush lived on the coastal wetlands where the sea interacted with rivers, being a littoral environment; ⑤24～10kaBP,the worst period of Quaternary natural environment, the south coastal plain of Laizhou Bay was dry grassland and loess deposition environment; ⑥10～4kaBP,owing to the warm and wet weather, sea level was high and transgression occurred; the local marine-deposited stratum embodied exuberant hydrophyte and aquatic plants. The maximal transgression of Holocene ended at 4kaBP;⑦4～0kaBP,the modern sedimentary environment which inclines to dry. Three warm and wet periods and two cold periods can be found. Of which, the warm period of 85-76 kaBP is corresponded with the late Yangkou seawater transgression and there is no evidence of early Yangkou seawater transgression, the warm period of 50-24kaBP is corresponded with the Guangrao seawater transgression and the warm period of 10-4kaBP is corresponded with Kenli seawater transgression, the duration of the latter one is longer than Bohai and east of Laizhou Bay. The three periods formed the foundation for the salt-water intrusion in this area.