Aptian综合年代地层事件:定量地层学的运用(英文)

INTEGRATED APTIAN CHRONOSTRATIGRAPHIC EVENTS: APPLIED QUANTITATIVE STRATIGRAPHY

以往发表的年代地层数据都是以Ma形式出现,以关键物种的首现面和末现面来界定的.一般而言,这些年龄是在用某种方法确定的某两个层的年龄基础上通过插值获得的,很大程度上仍然是估计值,而不是可以检验的科学结论.我们需要的是一个可以评价的、剖面重现的、标本重现的而且插值方法是经过严格检验的数据库.图形对比技术正是一个有用的方法,它可以综合众多剖面的分散分布的事件,并可以验证这些事件的顺序和年代.图形对比技术是一个定量的、非统计的方法,可以判别两个剖面之间存在的同时代关系.物种时限和非生物事件投点到X/Y图解上,时限可以通过对比线综合到单个的时间尺度上.其他剖面的数据通过重复以上过程把每个剖面的数据综合进来.获得的时限通过评价有这些物种出现的图形解而得到验证.Aptian阶(约124～112 Ma)时期环境发生巨大变化,用来确定Aptian阶的许多关键生物事件和年代地层事件并不都出现在同一个剖面.因此,这些事件的相对年龄始终是不确定的,也不是相关的.两个事件被提出来用于界定Aptian阶的底界,包括菊石Deshayesites tuarkyricus和磁极性带CM0.然而这两个事件标准地层剖面相隔600 km. 图形对比显示这两次事件出现在7万年间隔内.通过这一方法,来自23条Barremian-Aptian-Albian 期间的剖面被综合进入精确的数据库,可以用来评价和验证来自新剖面的数据.

Published chronostratigraphic data bases date the first and last occurrences of key species over a period of millions of years. Generally, the ages are determined by interpolation between horizons dated by different method. These ages are reliable estimates, but they are not testable. Therefore it is desirable that a data base be compiled that can be evaluated, sections re-collected, specimens re-examined, and the method of interpolation critically examined.Graphic correlation is also a useful methodology that integrates diverse events in numerous sections so that the relative order and ages of these events can be tested. Graphic correlation is also a quantitative, non-statistical technique that determines the coeval relationships between two sections. The ranges of taxa and non-biotic events in two sections are plotted on an X/Y graph, and the ranges are integrated into a single scale using the line of correlation. Data from additional sections are integrated by repeating this process for each section. The resulting ranges can be tested by evaluating each graphic solution in which the species are present. During the Aptian Stage(about 124～112 Ma)environmental conditions changed greatly. Many key bioevents and other chronostratigraphic events useful in defining the Aptian Stage do not occur in the same section. Thus, their relative ages are uncertain and not interrelated. Two events have been proposed to define the base of the Aptian, namely the ammonite Deshayesites tuarkyricus and the magnetochron CM0. However, they occur in sections more than 600 km apart. A graphic correlation experiment shows that they occurred within 70 000 years of each other. By this method, data from more than twenty-three Barremian-Aptian-Albian sections are integrated into a more precise data base that can be evaluated and tested with data from new sections.