雅鲁藏布江缝合带东段的放射虫与新特提斯洋的演化

The evolution of the Neo-Tethyan Ocean and the process of the India-Eurasia collision have been the hot topics on the earth science researches in Tibet Plateau. Although the recent studies on Neo-Tethys evolution have made a great progress, its opening time and the closing process as well as the timing of the India-Eurasia collision remains controversial. A kinds of rocks such as ophiolite, mélange and radiolarites etc., which may be the remnants of the Neo-Tethys along the convergence edge, are well exposed within the east Yarlung-Tsangpo suture zone (YTSZ) in the Zedong area, Southern Tibet. To date, there are still lack of systematic studies on radiolarians from these radiolarites. This project plans to undertake a systematic research on the biostratigraphy and paleobiogeography of the radiolarian fossils from various terranes in the Zedong area, to probe into the nature of the different radiolarian faunas and the characteristics of their assemblages, to widely compare them with that found in middle YTSZ or Tethys elsewhere in order to shed light on their stratigraphic and geographic distribution pattern and characteristics, to establish or improve a biostratigraphical framework in each terrane in this area, to recovery the sedimentary sequence of Neo-Tethys represented by these radiolarites, to provide the biostratigraphical constraints on some important events of the Neo-Tethys evolution, such as the ocean expansion and disappearance time, or even the Indian-Eurasian collision time. This study will help us to better understand the whole evolutional history of the Neo-Tethys Ocean in the east YTSZ.

有关新特提斯洋的演化和印度-欧亚大陆碰撞过程一直是青藏高原地球科学研究的热点。尽管近年来对新特提斯洋演化的研究已取得了很大进展，但对它的打开时间、闭合过程以及印度-欧亚大陆碰撞时间仍然存在很大争议。在藏南雅鲁藏布江缝合带东段的泽当地区有大量的和印度-欧亚大陆碰撞相关的蛇绿岩、混杂岩和放射虫硅质岩等出露，它们是新特提斯洋内汇聚边缘的残积物。至今，对硅质岩中的放射虫尚缺乏系统的研究。本项目将对该地区不同地体的放射虫做系统的生物地层学和古生物地理学研究，探讨其组合特性并与雅鲁藏布江缝合带中段及特提斯其它地区的放射虫进行广泛对比，以揭示它们在地层和地理上的分布规律，建立和完善该地区各个地体中的生物地层框架，恢复其所代表的新特提斯洋沉积序列，为确定新特提斯的扩张、消亡及印度-欧亚板块碰撞的时间等提供生物地层约束，从而有助于揭示新特提斯洋在雅鲁藏布江东段整个的演化过程。

有关新特提斯洋的演化一直是青藏高原地球科学研究的热点之一，关于它的打开时间、闭合过程等存在有很大争议。本项目主要对藏南泽当等地区的放射虫做了系统的生物地层学和古生物地理学研究，探讨了相关组合特性并与雅鲁藏布江缝合带中段、西段及特提斯其它地区的放射虫进行广泛对比，揭示了它们在地层和地理上的分布规律，建立和完善了该地区的生物地层框架，恢复了放射虫硅质岩所代表的新特提斯洋沉积序列，为确定新特提斯洋打开、扩张等的时间提供了生物地层约束，进一步揭示了新特提斯洋在雅鲁藏布江缝合带的整个演化过程。所取得重要结果有：.A．.在泽当地区建立了中三叠世晚安尼期到早诺利期8个放射虫组合（带），其中晚安尼期Oertlispongus inaequispinosus组合和Triassocampe deweveri组合是目前为止在雅鲁藏布江缝合带中发现的最早放射虫化石组合，很好地限定了西藏地区新特提斯洋的初始形成时间；.B．.在泽当近朗沟剖面，首次建立了中侏罗世阿林期、晚巴柔期和中巴通期的3个放射虫组合：即Laxtorum (?) jurassicum、Quarticella ovalis和Stichocapsa robusta组合。它们为雅鲁藏布江缝合带中深水沉积的地层对比提供了可靠的化石依据；.C．.在日喀则洛曲剖面硅质岩中，首次发现了早侏罗世普林斯巴期放射虫化石35属93种（包括1新种）。.D．.在普兰姜叶玛剖面，识别出早白垩世欧特里夫期至晚巴雷姆期的2个放射虫化石带和2个亚带：即Cecrops septemporatus带, Aurisaturnalis carinatus带, Aurisaturnalis carinatus carinatus亚带和Aurisaturnalis carinatus perforates亚带。