滇西昌宁-孟连带石炭-二叠纪䗴类之生物地层与古地理分析

The Changning-Menglian Belt in western Yunnan, China has been considered a suture zone of Tethys and also the demarcation between Gondwanan and Cathaysian realms. This belt thus is a crucial zone in China for studying the dynamic paleogeographic evolution of Tethys. As effective indexes for stratigraphic correlation and environmental reconstruction, fusulinid fossils can offer spatio-temporal evidence to explore the geological details of this belt. Nevertheless, only two published papers have conducted systematic study on fusulinids from this belt, since the geological survey in last century. This has resulted in a hitherto ambiguous understanding of taxonomic composition of these fusulinids, and directly impedes the progress of biostratigraphic analysis and paleogeographic interpretation. Detailed fusulinid biozonation has not been delineated in most areas yielding fusulinids in this belt, except at Yutangzhai in Yongde county and Shifodong in Gengma County. Besides, opinions of the paleogeographic indications of these fusulinids remain controversial. Accordingly to our preliminary investigation, the paleobiogeographic feature of the fusulinids in this zone dynamically changes through Permo-Carboniferous, when compared with their counterparts from blocks with Gondwana-affinity and Cathaysia-affinity. The general recognition of similarity between fusulinids from this zone and South China now cannot satisfy the goal for a more detailed geological anatomy of this suture zone. .Aiming to solve these issues, this project proposes to conduct a comprehensive study on the taxonomy, biostratigraphy and paleogeographic implications of fusulinids from this belt. Careful field observation would be firstly carried out on the Permo-Carboniferous carbonates and a large sum of fusulinid samples would be then collected from key sections. The collected fusulinid specimens would be systematically identified and described in order to clarify their taxonomic composition. Biozones will then be established in each measured section, based on the stratigraphic distribution of fusulinid taxa. A composite biostratigraphic sequence of fusulinids in this belt would be further synthesized and taxonomic feature be analyzed preferably at the time interval of each stage. .In order to improve objectivity and precision of assessment, qualitative and quantitative techniques would be combined to compare fusulinids from the Changning-Menglian Belt and those from Gondwanan and Cathaysian regions. The diversity and dominant genera or species would be emphasized for comparison. The major quantitative methods include similarity coefficient and cluster analysis. The selection of suitable similarity coefficients would be dictated by whether the dominant taxa in the dataset are cosmopolitan or endemic. Cluster analysis would be performed on generic level plus species data with distinct paleogeographic or biostratigraphic indications. Results of these analyses will be utilized to delve into the paleogeographic conditions of the Changning-Menglian Belt, such as sea-surface temperature, relative paleogeographic configuration. .The implement of this project not only can advance our understanding of fusulinids in the Changning-Menglian Belt, but more importantly shed lights on the evolution of Tethys recorded in western Yunnan, China.

滇西昌宁-孟连带是记录特提斯演化的关键地区，筳类能为剖析其地质过程提供时间和空间的约束。但自上世纪区调以来，仅有两篇文献系统研究了该带的筳类，导致目前对该带筳类属种组成的认识还不清晰，也从根源上制约了后续生物地层与古地理的分析。除永德鱼塘寨和耿马石佛洞以外，诸多该地区的含筳剖面都没有细致地划分筳类化石带。而且不同学者对该带筳类古地理意义的认识尚有一定分歧。我们初步分析揭示该带与亲冈瓦纳区、华夏区筳类组成的异同是动态变化的，且与华南的差异不容忽视，这些信息是了解该带古地理演化更多细节的很好切入点。因此，很有必要开展深入的野外考察和系统的化石鉴定，建立精细的筳类生物地层格架；结合定性对比与定量分析，尤其是优化的相似性系数和聚类分析，厘清各时期筳类组成特色，并探讨其古地理环境意义。这些工作不仅可以提升该带筳类的综合研究水平，也可为更清晰理解我国境内特提斯的古地理演化补充关键的古生物证据。

滇西昌宁-孟连带是特提斯域的关键构造带，被多数人解释为特提斯洋的主缝合带位置。论证古大洋存在的主要证据包括蛇绿岩，深海放射虫硅质岩和可能为海山沉积的灰岩。在这套石炭-二叠纪的灰岩中，具有时代和环境指示意义的䗴类化石丰富，但以往对其深入研究不够，例如对其古生物地理属性尚存一定的争议。因此，本项目聚焦该带石炭-二叠纪䗴类化石，通过详细的野外考察、剖面实测和样品采集，开展系统古生物学，生物地层学和古生物地理学分析，以期为昌宁–孟连带的古地理演化补充重要的约束。实测了晚石炭-早二叠世剖面2条（安信槽剖面和芒阳剖面），建立了䗴类化石带Triticites富集带，Spheroschwageria sphaerica带，Eoparafusulina富集带和Chalaroschwagerina solita带；中二叠世剖面1条（李子树剖面），建立了Misellina pamiriensis组合，Neoschwagerina brevis组合和Neoschwagerina margaritae组合；晚二叠世剖面1条（石佛洞剖面），识别了Codonofusiella kwangsiana组合和Palaeofusulina sinensis组合。可见，带内化石面貌和生物地层序列可与华南地区很好的对比，与中高纬度的冈瓦纳北缘地区迥异。利用定量统计分析进一步证实，如稀疏标准化和聚类分析等，该带䗴类的早二叠世的属级多度在95%的置信水平显著低于华南地区。䗴类属种组成所反映的信息，与以往将这套灰岩解释为海山的认识一致，并能更精细的揭示该海山的古地理位置在当时远离冈瓦纳北缘，处于华夏区内但古纬度略高于华南。综合地层学和沉积学证据，推测昌宁-孟连带的主体部分在晚古生代时期，位于西侧保山地块的被动陆缘。含䗴的海山灰岩可能是对于大面积出露的碎屑岩地层而言为外来岩块，在特提斯关闭时期自东向西推覆就位到现今的位置。项目的研究成果细化了昌宁–孟连带䗴类生物地层序列，进一步厘清了化石组成的古生物地理属性，并提出了该带晚古生代古地理格局的阶段性新认识。从古生物地理学角度，特提斯域陆架浅海的化石研究相当充分，但洋盆内部海山环境的资料和认识明显薄弱，因此本项目所掌握的化石资料和分析结果也为弥补这一薄弱环节补充了可靠的信息。