松辽盆地晚白垩世轮藻生物地层划分与对比

Cretaceous plays a significant role during the sweep of geologic history in light of some major events such as global warming and vast distinction. In recent years, with the international chronostratigraphy standard gradually established, marine Cretaceous seems to be well observed. However, the non-marine Late Cretaceous is still poorly studied mainly because there is a lack of comprehensive record, and in part because research about Charophyta, the best instrument of dating numerous non - marine strata, in particular those of the Cretaceous and valuable tool for intercontinental correlation according to Gramast (1972), has been neglected. Songliao Basin in northeastern China is one of the largest Cretaceous continental rift basins in the world where the hole of Songke-1 (SK1)is located in the centre. It provides successive and detailed materials to research paleoenvironment and paleoclimate of non-marine cretaceous setting. Therefore, this study will focus on the classification and correlation of Late Cretaceous by means of Charophyta and other fossils found in the core. The target interval in this scenario is from the upper Quantou Formation to the Mingshui Formation deposited during the depression stage in the Cretaceous. Based on the high-resolution sampling from SK1 and the outcrops across the basin, it's hoped to classify the complete charophyta assemblages during Late Cretaceous. Meanwhile, according to the previous studies and other microfossils related, together with the analysis about biostratigraphy, lithostratigraphy, magnetostratigraphy and event stratigraphy, this study aims to discuss the age of the upper Quantou Formation, Qingshankou Formation, Yaojia Formation, Nenjiang Formation, Sifangtai Formation and Mingshui Formation respectively. Furthermore, the division scheme of Lower - Upper Cretaceous boundary and K/Pg boundary will be analysed in details as well. What's more, various parameters of the paleo-Songliao basin including lake level, salinity, and hydrodynamic condition will also be mentioned if poddible in this study from the perspectives of sedimentary and trace-elements of ostracode shells, which helps to identify the background information of some significant geological events.

目前，松辽盆地晚白垩世地层古生物研究主要借助介形类、孢粉和沟鞭藻等化石；而轮藻化石作为"白垩纪-古近纪地层时代确定的最佳手段、洲际陆相地层对比的有用工具"（Fairbridge and Jablonski,1979），研究相对薄弱，缺乏连续的地层序列。晚白垩世是轮藻地史上的最大繁盛期之一，使其成为陆相地层划分与对比的重要依据。本项目将选择松辽盆地白垩系科学钻探连续取心资料作为主要研究对象，建立晚白垩世轮藻地层序列，划分以轮藻为主的古湖泊生物群的演化阶段，标定各个阶段的化石组合特征，明确区域年代地层各单元底界的生物定义，并结合不同门类的生物地层学特征和相关学科的资料，努力实现轮藻地层与国际地层标准的对比。本项研究通过深化已有地层学成果，将进一步恢复生物的演替在松辽盆地的记录及环境背景，为完整地反映晚白垩世陆相微体生物群特征、揭示重要界线地质事件的标记提供更多依据。

本项目按照计划执行，以之前研究相对薄弱的轮藻化石为主要对象，基于松辽盆地白垩系科学钻探连续的取心资料，重点对南孔钻遇的泉头组上部至嫩江组下部微体化石的纵向分布特征进行分析，标定了各个阶段的化石组合特征，明确了区域年代地层各单元底界的生物定义，建立了松辽盆地晚白垩世轮藻地层序列，开辟了海相-陆相对比的新渠道。. 项目组结合不同门类的生物地层学研究，通过深化已有地层学成果，恢复了生物演替在松辽盆地的记录及环境背景，建立了可与全球年代地层标准对比的生物-年代地层格架，进一步实现了轮藻地层与国际地层标准的对比，为揭示重要界线地质事件的标记提供了更多的依据。经过野外对地表剖面的考察和采样以及室内样品的处理，我们划分、完善了以轮藻为主的湖泊生物群的演化阶段，重新标定了相应序列和化石组合特征，确定了泉头组上部至姚家组的地质时代和两个界线的位置：泉头组上部为Aptian 晚期–Turonian早期，青山口组处于Turonian期－Coniacian期，姚家组相当于Santonian期- Campanian期；Aptian期 – Albian期界线位于泉三段内，以Mesochara symmetriea在深度1911.1米的末现面为标志；Albian期-Cenomanian期即上、下白垩统界线位于泉四段内，以Euaclistochara mundula在深度1795.44米的末现面为标志。这两处界线位置的确定是基于松科1井南孔化石提出的初步认识，更大区域范围的分布情况还有待继续研究。.项目组发表了经过标注的期刊、会议论文各一篇（还有一篇第一标注的期刊论文正在审稿），获奖一项，培养博士后一人，多次在国内外学术会议上与各国专家学者们交流了研究成果。此外本项目还对古生态学做了初步的分析，从藻类演化角度恢复了古松辽湖泊的部分信息，这对于更加完整地反映陆相微体生物群的特征、进一步恢复湖盆的古环境有着重要作用。