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    山东莱州湾南岸晚上新世以来（6.8~0.004 Ma）古植被演替与海平面波动

    Late Pliocene（6.8−0.004 Ma）vegetation evolution and sea−level fluctuations on the southern coastal plain of Laizhou Bay, Bohai Sea, China

      摘要
    • 摘要:
      研究目的 海岸带沉积物中的微体古生物化石保存着丰富的地质环境信息，本文的目的是重建莱州湾南岸晚上新世以来的古植被演替与海平面波动关系。
      研究方法 拟通过对HLL01钻孔的孢粉、淡水藻类、海相沟鞭藻、有孔虫内衬等微体古生物化石的分析，恢复和重建莱州湾南岸及其附近地区晚上新世以来的古植被演替与海平面波动。
      研究结果 （1）在晚上新世—早更新世阶段（约6.8~1.6 Ma），大量的陆生草本花粉（75.13%）指示研究区的植物群落主要以藜科、蒿属及禾本科为主的草原植被，气候温暖偏干。（2）在早更新世—中更新世阶段（约1.6~0.6 Ma），研究区的植物群落开始由草原向森林草原类型过渡；急剧增加的淡水藻类，则指示研究区可能有大的河流注入，或形成较大规模的湖泊；降水量增加，气候变得湿润。（3）在中更新世—晚全新世阶段（约0.6~0.004 Ma），研究区的植物群落已经变成森林草原植被。淡水藻类含量略有降低，指示研究区的河流注入量开始减少，湖泊面积也开始萎缩。同时，海相沟鞭藻和有孔虫内衬等海相化石记录，指示研究区在该阶段出现了较为明显的大规模海侵事件。
      结论 莱州湾晚上新世以来发生了3次古植被演替与海平面波动事件。

       

      Abstract:
      This paper is the result of coastal geological survey engineering.
      Objective Microfossils, especially pollen, spores, and dinoflagellate cysts, as direct indicators or proxies, provide significant information on geological environment. Therefore, palynological analysis has an important role in restoration and reconstruction of vegetation history and sea−level fluctuations, which provides information from the sediment cores, especially in alluvial coastal plain regions.
      Methods In this study, we carry out analyses using detailed palynological records of pollen, spores, freshwater algae, marine dinoflagellate cysts, and foraminiferal organic linings from Borehole HLL01 on the southern coastal plain of Laizhou Bay, Bohai Sea, northern China.
      Results The results provide valuable information on vegetation history and sea−level fluctuations since the Late Pliocene. Large amounts of terrestrial herb pollen (75.13%; mainly composed of Chenopodiaceae, Artemisia and Poaceae) were identified at Borehole HLL01, suggesting that coastal steppes flourished in the study area and its adjacent areas, and a cold and dry climate than the present during the Late Pliocene to Early Pleistocene, ca. 6.8−1.6 Ma. After that, the steppe areas began to shrink, and the transition of coastal steppes to forest grasslands occurred in the Early−Middle Pleistocene, ca. 1.6−0.6 Ma, indicating a warm and humid climate. A sharp increase in freshwater algae indicates that large rivers’ discharge had been injected into the study area, or large lakes were formed. Afterward, relatively cool and dry climatic conditions appeared, with little precipitation, and a relatively significant transgression event revealed by dinoflagellate cysts and foraminifera organic linings, and forest grassland vegetation was distributed in the study area and its adjacent areas, during the Middle Pleistocene to Holocene, ca. 0.6−0.004 Ma.
      Conclusions Three ancient plants have occurred and the sea level fluctuations occurred since the Late Pliocene (6.8−0.004 Ma) in the Laizhou Bay.

       

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