塔里木盆地塔中台地奥陶系海百合茎化石丰富。本文通过研究塔中 35 井上奥陶统良里塔格组和桑塔木组岩芯中的海百合与其共生生物的关系, 讨论了海百合化石的古生态。在塔中 35 井上奥陶统取芯中识别出 7 种海百合茎类型: 圆圆茎、星星茎、星圆茎、椭圆圆茎、星椭圆茎、圆角星星茎和不规则星茎, 根据茎板形态划分为五射茎板组(Pentameri)、椭圆茎板组(Elliptici)、圆茎板组(Cyclici)、特殊茎板组(Varii)四种组合类型; 统计了海百合茎化石各种切面的大小和百分含量; 结合岩性分析了每段地层的沉积环境。研究发现, 在局限泻湖环境下, 蓝细菌–四分珊瑚为主的生物组合中不见海百合化石碎片; 仅见腹足类和介壳类化石的细砂屑滩中, 偶见细小的海百合茎化石; 在开阔海环境中, 海百合广泛与苔藓虫、管孔藻、粗枝藻等共生。在海百合–苔藓虫组合中, 海百合茎板的类型最丰富多样, 五射茎板组、椭圆茎板组、圆茎板组、特殊茎板组等四种茎板组合类型都存在; 在管孔藻–海百合组合中, 海百合茎板主要为圆茎板类型, 粗大、密集, 海百合茎碎片含量最高; 在海百合–粗枝藻组合中, 海百合茎板的数量减少、大小变小, 但茎板的类型比较丰富, 四种茎板组合类型都有。由此认为, 塔中台地上奥陶统沉积期, 海百合生长的首选环境为开阔台地, 并受水动力能量和水体清洁度控制: 水动力能量高, 水体清洁, 海百合繁盛; 水动力能量低, 水体动荡浑浊, 海百合可以生存; 水动力能量低、较为动荡、微生物席发育的环境, 不利于海百合生存。

Crinoid fragments and ossicles are very common in Ordovician carbonate rocks of the Tazhong Platform, Tarim Basin, Northwest China. In this paper, which differs from the previous studies that focused on intact crinoid fossils, we present a comprehensive analysis of the types and contents of the crinoid stem fossils including ossicles and fragments, and the taphonomy of the symbiotic animals from the Upper Ordovician core of Well Tazhong 35, as well as the sedimentary environments in order to understand the paleoecology of the crinoids. From the core samples, seven types of ossicles are identified: Cyclocyclicus, Pentagonopentagonalis, Pentagonocyclicus, Ellipsocyclicus, Pentagonoellipticus, round Pentagonopentagonalis, and irregular Pentagonopentagonalis. Four ossicle assemblages are recognized: Pentameri, Elliptici, Cyclici and Varii. Results of the statistic analysis of the shape, size and percentage of the ossicles, combined with the taphonomic characteristics of the symbiotic animals and analysis of the sedimentary environments, indicate that crinoids are absent from the community dominated by cyanobacteria and tetradiids in the restricted lagoon environment. Very few slim crinoid ossicles occurr in the biota of gastropods and ostracods in the fine-grained bank facies covering the lagoon facies. Abundant crinoids and various symbiotic bryozoans, Solenopora, dasycladaceans and other organisms are present in the biota of the open platform facies. Both crinoids and bryozoans are filter feeders, and should have a symbiotic but competition relationship in most cases. However, in the Ordovician Tazhong sea, the difference in their body size determines the two groups belong to different filter feeding groups, which eases the competition between them. In communities dominated by crinoids and bryozoans, crinoid ossicles are the most abundant, and all four ossicle assemblages are present. Solenopora is photosynthetic, it has no competition with the crinoids, and its relationship with the crinoids is mutualistic. The crinoid ossicles in the Solenopora–crinoid community belong to the Cyclici type. They are relatively simple, big, and dense, and their content is the highest. The crinoids are widely symbiotic with the dasycladaceans. Due to the influence of the oncoids formed by filamentous cyanobacteria, the number and size of crinoid ossicles and fragments are smaller than those of the dasycladaceans, but they are relatively richer and more diverse, including all four types. Therefore, we suggest that the most suitable environment is the open platform for the Upper Ordovician crinoids from Well Tazhong 35, and the main controlling factors are hydrodynamic energy and water cleanliness. The crinoids flourish more in cleaner water with higher hydrodynamic energy, while turbulent water with low hydrodynamic energy is disadvantageous to their survival.

河北地质大学教改项目(2021J44)资助