河套盆地东部第四纪中晚期介形类特征及其沉积环境意义

根据河套盆地东部DTLC孔介形类组合及其岩性、岩相的分析，着重地探讨了该区第四纪中、晚期介形类的生物地层特征及其沉积古环境意义。研究认为:中更新世早期（Q₂1），未见介形类，以冲洪积沉积环境为主，兼有河湖交替演化；中更新世晚期（Q₂2），介形类生物组合为Leucocythere plethora-Eucypris inflate-Limnocyther dubiosa，推测为封闭性的半咸水、咸水湖相沉积环境，气候偏冷；晚更新世早期（Q₃1），介形类生物组合为Leucocythere plethora-Limnocythere dubios，反映了封闭性的半咸水深湖相沉积环境；晚更新世晚期（Q₃2），少见淡水介形虫化石，以Ilyocypris manasensis-Candoniella albicans-Cypria luminosa为组合特征，反映了以河流冲洪积环境为主；全新世（Q₄）为河流沉积环境。通过河套盆地区域沉积环境的综合分析认为:中更新世晚期（Q₂2）至晚更新世早期（Q₃1），河套盆地为封闭性内陆湖盆，黄河为内流河；自晚更新世晚期（Q₃2）以来，黄河逐渐地转为外流河，河套盆地为外流湖盆。 

Ostracod characteristics of the eastern Hetao Basin and its sedimentary environmental significance during the Middle and Late Quaternary

By the comprehensive analysis of lithology, lithofacies and ostracod biological assemblages of the DTLC core in the eastern Hetao Basin, the ostracod biostratigraphy and its sedimentary environmental significance during the middle and late Quaternary was emphatically discussed. The conclusions are as follows:In the early stage of Middle Pleistocene (Q₂¹), it reflected a fluvial-lacustrine alternative sedimentary environment mainly dominated by alluviation with no ostracod fossils. In the late stage of Middle Pleistocene (Q₂²), it reflected a closed brackish and salt water lake environment under cold and dry climatic condition with a brackish-salt water lacustrine ostracod enrichment characterized by Leucocythere plethora-Eucypris inflate-Limnocyther dubiosa. During the early period of Late Pleistocene (Q₃¹), it represented a closed brackish water and deep lake environment with a relative lacustrine ostracod enrichment characterized by Leucocythere plethora-Limnocythere dubios. During the late period of Late Pleistocene (Q₃²), it mainly reflected an alluvial-proluvial environment with a small number of freshwater ostracods characterized by Ilyocypris manasensis-Candoniella albicans-Cypria luminosa. It was a river-floodplain environment during the Holocene (Q₄). According to the comprehensive analysis of the regional sedimentary environment of the Hetao Basin, it is concluded that the Hetao Basin was a flows-in lake basin where the Yellow River was an inner river from the late stage of Middle Pleistocene (Q₂²) to the early period of Late Pleistocene (Q₃¹). Since the late period of Late Pleistocene (Q₃²), the Yellow River gradually turned into an outflow river and the Hetao Basin became an outflow lake basin.