中文摘要：

晚奥陶世赫南特贝动物群在空间上随水深和温度等环境梯度变化的分布型式已经得到广泛而深入的研究,但对该动物群在纵向上演变型式的研究还比较缺乏。以四川长宁双河上奥陶统观音桥组的赫南特贝动物群为研究对象,分析了该动物群的腕足动物个体密度和多样性演变趋势以及与水深、氧含量和生物扰动等环境因子的协同变化,探讨了动物群演变与环境变化之间的关系。研究表明,多样性和个体密度在观音桥组整体上呈上升趋势,最后整个动物群快速消亡,而氧含量和生物扰动强度总体上也呈增加趋势。奥陶纪末冈瓦纳大陆冰川的扩张所导致的全球海平面下降可能是影响赫南特贝动物群演变的主要环境因素,但氧含量的突然降低和生物扰动强度的增加也会对群落的一些特征产生影响,有时甚至成为重要的控制因子。赫南特贝动物群多样性在观音桥组顶部达到峰值,但随着海平面的突然下降迅速消亡,相比较其从下而上多样性逐渐增加的过程而言要迅速得多。

英文摘要：

The spatial distribution of the latest Ordovician Hirnantia fauna in relation with the water depth and temperature gradients has been studied extensively and throughly.However,there has been no specific investigation on the temporal changes of the Hirnantia fauna.Based on the samples from the Kuanyinchiao Formation at Shuanghe,Changning County,southern Sichuan Province,China,we analyze the palaeoecological changes of the Hirnantia fauna using taxonomic diversity and individual density,and the environmental changes in relation with the water depth,oxygen concentration and bioturbation levels throughout the Kuanyinchiao Formation.We also discuss the relationships between the community changes and environmental fluctuations.It shows that community diversity and individual density of the Hirnantia fauna generally increased through time and decreased sharply near the top of the formation immediately after the taxonomic diversity reached its peak.Gradual changes of many environmental factors with the glaciation-induced sea level drop might account for the general palaeoecological trends of the Hirnantia fauna,and later sudden rising of sea level might be the cause of the rapid disappearance of the fauna,but the fluctuation of oxygen concentration or bioturbation levels might alter the structure of brachiopod community dramatically in some situations. This study is based on one locality which was in the deeper water environment during the latest Ordovician.Previous studies show that temporal change of the Hirnantia fauna in the shallower water settings might have different patterns,but no specific studies were done at this particular site.Later investigation should compare the temporal patterns of Hirnantia fauna in different areas and under different environmental settings.All these works would contribute to understand how the Hirnantia fauna survived and developed in the relatively stable period between two episodes of the end Ordovician mass extinction.