Taphofacies models for Upper Cretaceous ammonoids from the Kotanbetsu area, northwestern Hokkaido, Japan
Taphofacies models for Upper Cretaceous ammonoids from the Kotanbetsu area, northwestern Hokkaido, Japan
复制标题
日本北海道西北部小丹别地区上白垩统菊石的地相模型
DOI：
10.1016/s0031-0182(03)00486-3
复制
发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Ryoji Wani
中科院分区：
文献类型：
--
作者：
Ryoji Wani
根据沉积相特征，阐明了日本北海道西北部小丹别地区上白垩统菊石壳的埋藏属性。主要属性是：（1）破碎率和碎片分离率;（2）菊石大小分布和平均大小的模式;（3）钙质结核中贝壳的浓度;（4）异形菊石的出现;（5）个体总数和物种多样性。这些属性被划分为四个出露相，分析得出以下认识：破碎率和碎片分离率增加向浅环境，因此，这些指标将主要反映能量水平和改造事件的频率。风暴主导的陆棚环境中，贝壳是如此丰富的集中，贝壳浓度将形成风暴和后续的改造事件。个体总数和多样性指数在四种出露相中存在差异，外陆架上部个体数和多样性指数最大。这些趋势被推断为复杂地反映了环境条件，如能量水平，返工事件的频率和海平面变化。
The taphonomic attributes of ammonoid shells in the Upper Cretaceous of the Kotanbetsu area, northwestern Hokkaido, Japan, are elucidated with reference to sedimentary facies. The major attributes are: (1) fragmentation rate and fragment-separation rate; (2) patterns of ammonoid-size distribution and mean size; (3) shell concentration within calcareous concretions; (4) the occurrence of heteromorphic ammonoids; and (5) the total number of individuals and species diversity. These attributes are classified into four taphofacies, analysis of which has lead to the following insights: the fragmentation rate and fragment-separation rate increase toward shallower environments; thus, these indices would chiefly reflect the energy level and the frequency of reworking events. Shells are so abundantly concentrated in storm-dominated shelf environments that shell concentrations would be formed by storm and following reworking events. The total number of individuals and the diversity differ among the four taphofacies: these indices are the largest in the uppermost part of outer shelf. These tendencies are inferred to complexly reflect environmental conditions, such as energy levels, frequency of reworking events, and sea-level changes.