海洋底栖古群落演替模式——以华蓥山茅口组腕足动物群落为例

Successional pattern of marine benthonic palaeocommunityTaking the brachiopod community of Maokou stage in Huaying Mountain as a case

以热力学理论和信息熵原理为基础,分析了古群落的热力学本质和信息熵的内涵,指出古群落演替可分为4个阶段:开始阶段、发展阶段、顶极阶段和衰退阶段。不同阶段具有明显不同的信息量(信息熵),信息熵为最大值阶段也就是古群落最复杂、最无序的顶极阶段。为此,可利用这一特性对地层进行高精度的划分和对比。经研究,初步总结出5条判别古群落演替不同阶段的基本原则:①地层层序率原则;②生物演进原则;③信息熵最大原则;④物种多样性指数呈对数正态分布原则;⑤古群落取代原则。在以川东华蓥山地区茅口期腕足动物群落演替分析的实例中,选择了4个统计量作为计算反映古群落结构特征信息熵的参数,即物种多样性指数(d)、物种个体平均大小(g)、物种生物量(s)及物种平均凸度(t),对两个古群落不同演替阶段的信息熵进行了计算和讨论,指出本地区茅口组地层分为上下两段,下段还可以分为3个亚段。同时发现在没有突发事件的影响下,古群落演替以衰退阶段历时最长,大约是顶极阶段的6～8倍。

Based on the thermodynamics theory and the information entropy principle and on analysis of the intrinsic of thermodynamics and the connotation of information entropy of the paleocommunities, the present authors pointed out that the evolution of a paleocommunity can be divided into four stages: beginning, developing, summit and declining. Different stages have obviously different amount of information (information entropy), and the biggest information entropy corresponding to the most complicatedly and disorderly summit stage of the paleocommunity. For this reason, the authors can make use of this character to demarcate and contrast geologic strata in a high accuracy. Five basic principles were recognized for distinguishing the paleocommunity at different stages: ① the principle of the sequential stratigraphy, ②the principle of biological evolution, ③the principle of biggest information entropy, ④the principle of the exponential of species variety with logarithmic normal distribution, ⑤ the principle of paleocommunity replacement. During analyzing the case of brachiopod community succession of the Maokou stage in the Huaying Mountains in the east of Sichuan, the authors have selected four statistics parameters for calculation of the information entropy of the two sets of the palaeocommunities: exponent of species variety (d), average size of individual of the species (g), mass of the species (s) and average convex-level of species (t). The result reveals that the local strata of the Maokou Formation can be divided into two members: the upper and the lower. The lower member can be further divided into three sub-members. The decline stage lasts the longest (approximately 6～8 times of the summit stage) during the evolution of the palaeocommunity when no the impact of the burst events was found.