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Biohorizon

Release date:2017-07-26  Browse times:1482
     生物面是指在其上、下生物地层特征有重要而显著变化的一个面,或本身具有独特生物地层特征的一个薄层,因而被普遍作为一个生物地层单位的界线使用,它也可以出现于生物地层单位之中。生物面也称界面(Surfaces)界线(Boundaries)、标志层(Markere)、基准面(Datum planes)及关键面(Key horizons)等。

 生物面最有对比(不完全是时间对比)价值。在建立生物地层单位、进行底层对比和分统划阶过程中,首先要寻找出合理、明显而又分布广泛的生物面。
  
       建立生物面所依据的特征通常是,以一个一直地层剖面为基础的生物分类单位的首次出现(first appearance)、最后出现(last appearance)、最低存在(lowermost occurrence)、最高存在(uppermost occurrence)、明显存在、频率及丰度变化和单个分类单位(individual taxons)的变化特征(如有孔虫壳体旋向改变,或珊瑚数目或排列方式的改变)。其中,首现基准面(FADS)和未现基准面(LADS)均为常用的生物面。

 
 
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