高邮凹陷深凹带戴南组古生物特征及环境意义

Paleontological Features and Sedimentary Environment of Dainan Formation in Deep Sag of Gaoyou Sag

充分利用岩芯和古生物分析资料,结合沉积相研究成果,对高邮凹陷深凹带戴南组一段—二段5亚段的介形虫和轮藻化石及其沉积环境的关系进行系统研究。识别出介形虫70个属种,统计显示以金星介科分子为主,其次是玻璃介科分子,还有少量胡花介科分子,其化石组合的垂向变化反映了戴南期湖泊水体从半咸水→淡水—微咸水→半咸水→淡水的旋回性变化。发现轮藻化石76个属种,主要有常州厚球轮藻、强壮冠轮藻、长柱形钝头轮藻、小球状轮藻等,其中以戴一段一亚段最为繁盛,表明当时较为稳定的半咸水—淡水沉积环境。介形虫化石组合和轮藻化石的垂向分布和演化与沉积环境、沉积相变迁和分布具有密切关系。介形虫组合以淡水—微咸水环境中的属种占优势,且轮藻勃发时,反映陆源碎屑物质供给充足,沉积相以加积型或进积型三角洲和扇三角洲为主;当介形虫组合以半咸水环境中的属种占优势时,表明陆源碎屑物质供给较弱,沉积相以退积型三角洲和扇三角洲为主。

Based on rock core and paleontology analyses data, combined with the sedimentary facies, the relationship between fossils, such as ostracods and charophytes, and the sedimentary environment of the first and second members of the fifth sub-member of the Dainan Formation in the Deep Sag of Gaoyou Sag were systematically analyzed. Seventy species of ostracods were identified, with the Cyprididae Baird section molecules being dominant, followed by Candonidae Kaufmann,and a small number of Limnocytheridae. The vertical variation in the fossil assemblage reflects the cyclic changes in the lake water during the Dainan Period, namely, brackish water→fresh water→brackish water→brackish water→fresh water. In addition, 76 species of charophytes were identified, including Grovesichara changzhouensis, S tephanochara fortis, Obtusochara longscoluminania, and Sphaerochara parvula. The first sub-member of the first member of the Dainan Formation is most prosperous, which manifests a quiet and brackish-fresh water environment during those periods. The vertical distribution and evolution of the ostracods and charophytes fossil combination has a close relationship with the changes in and distribution of the sedimentary environment and facies. When the ostracods fossil assemblage in fresh to brackish water is in a dominant position and the chara is flourishing, it indicates that terrigenous clastic sediment is abundant. Additionally, the sedimentary facies are dominated by aggradation or a progradation delta and fan delta. When the ostracods fossil assemblage in brackish water is in a dominant position, it indicates that the terrestrial sources are short of clastic substance supply, and the retrogradation delta and fan delta are the main sedimentary facies