黄旗海介形类及其壳体稳定同位素环境记录

利用黄旗海冬季坚固的冰封面作为稳固的司钻平台 ,在湖泊中央成功地获取了高质量的湖底连续沉积岩芯。对其中长 1 1m的HQH4岩芯中的介形类化石进行了属种古生态和壳体稳定同位素研究。结果显示 ,在 1 0 2 0 0aB .P .前后黄旗海进入了稳定的湖泊阶段。在此之前 ,介形类的丰度极低。介形类的最大丰度出现在 1 0 2 0 0 -680 0aB .P .,反映了早全新世期间黄旗海较高的生物生产率。在此期间 ,介壳的δ18O值的变化范围较大 ,反映了黄旗海水体氧同位素组成在全新世早期的变幅较大。从 680 0aB .P .起 ,介形类的丰度突然大幅度降低 ,介壳δ18O值随后降低 ,反映了中全新世黄旗海湖水变深 ,湖底还原性显著增强。从 3 2 0 0aB .P .起 ,湖泊水位显著下降 ,湖底氧化条件明显增强 ,介形类的丰度继续下降 ,直到大约 1 3 0 0aB .P .才出现回升

Lake Huangqihai,Inner Mongolia:a Palaeoenvironmental Record Deduced from Ostracoda and Stable Isotope Composition of Ostracode Shells

The successful recovery of 3 sediment cores,each with 11m long,from the middle of Lake Huangqihai is the first practice of the "off the-ice coring technique" for lakes in China Core HQH4, one of the 3 cores, was used for the investigation of ostracoda palaeoecology and stable isotope geochemistry of ostracode shells Results suggest that the appearance of the ostracode started from about 10200 a B P , from which Lake Huangqihai began to be a constant lake environment The abundance of ostracode shells was extremely low in the sediments deposited before 10200 a B P Maximum abundance occurred in the early Holoene between 10200 and 6800 a B.P., reflecting the highest biological productivity of the lake The ostracode δ 18 O values of early Holocene varied in the range from -4 64‰ to 2 46‰, suggesting a large range of variation in δ 18 O of the lake water At about 6800 a B P , an abrupt decrease in ostracode abundance was followed by a sharp decrease in δ 18 O ostracode This suggests a deepened lake environment with much more reduced conditions at the lake bottom during 6800 and 3200 a B P From about 3200 a B.P., Lake Huangqihai decreased in lake-level, and ostracode abundance continued to decrease, and then increased around 1300 a B P as the redox conditions of the lake bottom turned to be less reduced