用序列优化和测评法探讨生物地层事件的最优分带和对比

RANKING AND SCALING BIOSTRATIGRAPHIC EVENTS NEAR PER- MO-TRIASSIC BOUNDARY IN SOUTH CHINA

本文以华南二叠-三叠系界线地层的30个剖面的资料为基础,用序列优化和测评法研究44个生物地层事件的顺序、分带和对比。序列的优化有两种方法。Hay法和拣分法近来被强调是较好的方法,本文用这两种方法对资料进行了序列优化,然后以两个优化的序列用测评法计算相继事件之间的距离系数,并作聚类图(图1)。在比较这两个序列及其聚类结果的基础上,本文划分了六个生物带和两个亚带。对这些生物带在30个剖面中的位置及它们在剖面间的对比,文中作出了分析(表4),尤其是用正态性检验对生物带的对比作出了恰当的评价。

The purpose of this paper is to develop an optimum sequence and to erect a zonation synthesized from the sections mostly measured by P-T Boundary Research Group of China University of Geo-sciences. Two ranking techniques, the presorting option and the modified Hay method, are better methods recently emphasized by several geologists . Based on these two methods, two sequences, I and I , are gotten and shown in Table 1. The purpose of the scaling method is to calculate 'distances' in time between successive events after an optimum sequence is constructed. Both sequences (Order I obtained by the Hay method and Order I -by the presorting option) are respectively used as starting points for scaling in order to compare the scaling results. The outputs of calculating 'distances' of the two sequences are shown in Table 3. In general the two sequences possess more similarities than differences between groups of biostrati-graphic events in the two dendrograms (Figure 1) , even though the relative relationships between successive events are different within the groups. The two optimum sequences at the same time can be divided into six groups according to the two principal reasons;They have the same events within a group (comparing the two sequences) and the events with the shorter distances should be firstly clustered into a group. Based on these six groups six biozones and two subbiozones are named. The results of biozone correlation in light of the ranking and scaling techniques are very good when compared with the study using other methods before.