早—中奥陶世之交笔石动物群全球分布及其控制作用

Global Distribution of Graptolite Fauna and Its Controlling Factor During the Lower-Middle Ordovician Transitional Period

为研究笔石动物群在早-中奥陶世之交全球分布的控制因素,从以下3个方面进行了分析和研究:①分析了穿越扬子地台笔石动物群的分布特征;②在对笔石体形态功能分析的基础上,探讨了水体深度对笔石动物群分布的影响;③根据当时的古地理格局,并参考现今的洋流分布,建立了早—中奥陶世之交的洋流分布图。在以上研究的基础上,对前人以水体深度作为控制这一时期笔石动物群分布的关键因素的假说提出了质疑,并认为笔石动物群的分布在很大程度上受控于洋流的作用,而洋流的形成和当时的古地理格局有着密切的关系,换言之,是古地理格局和洋流作用共同控制了笔石动物群的总体分布面貌。

In order to study the controlling factors on the global distribution of graptolite fauna during the Lower-Middle Ordovician transitional period,the authors analyze the following data：（1）the distribution characteristics of the graptolite fauna trans-Yangtze platform,i.e.from basin facies to carbonate platform facies,and the transitional belt in between;（2） the influence of water depth on the distribution of graptolite fauna based on the morphological function analysis of the graptolite rhabdosome;（3） the global oceanic currents distribution model based on the paleogeography during that period and the oceanic currents model nowadays.Consequently,the authors doubted the hypothesis that the control factor for the distribution of graptolite fauna during this period is the water depth proposed and accepted by most predecessors.It is concluded that the graptolite distribution of the Lower-Middle Ordovician transitional period is controlled by oceanic currents.The formation of the oceanic currents is close related to the geographical changes.Therefore,it is reasonable to consider that the paleogeography and the oceanic currents together controlled the graptolite distribution.