地层剖面的完整性估测及其地质意义

COMPLETENESS ESTIMATION OF STRATIGRAPHIC SECTIONS AND ITS SIGNIFICANCE

地层完整性是指剖面上所有沉积物代表的总时间与地层剖面代表的总时间之比。由于地层剖面中或多或少地发育有沉积间断，因此地层剖面的完整性是一个大于０小于１的小数。如何准确地测定地层剖面的完整性是目前仍未能解决的地质学难题，近十余年来，国外有许多研究者潜心于这一领域的研究，从不同的角度提出了各自的测定方法，这些方法包括：长期／短期沉积速率比值法、剖面厚度／全球同期平均沉积厚度比值法、潜穴化石定性估测法以及古地磁法等。尽管这些方法各有其不足之处，但却为今后的研究打下了坚实的基础。地层剖面的完整性对于沉积环境解释、生物演化模式分析、事件性及幕式沉积作用研究等有着重大的影响；地层剖面的不完整性严重阻碍了年代地层对比精度的提高。笔者认为，只有以高分辨率事件地层学和旋回地层学为基础的，综合生物地层学、磁性地层学。

The completeness of a stratigraphic section is defined as the fraction of time intervals of some specified length(t) that have left a record.The completeness of any section has a probabilistic character that it must take a value between one and zero because of the occurrence of hiatus.How to determine the completeness of a section is an unsolved difficult problem.Last ten years and more,several researchers proposed a few approaches to completeness determination such as ratio of long and short term sedimentation rates,compared thickness of a section with global average accumulation for that timespan,tiered trace fossils and paleomagnetic data methods.Despite some special requirements and limitations,these methods provide a firm fundation for future work.The completeness of a section plays an important role in interpretation of sedimentary facies,pattern analysis of organic evolution and studies of event or episodic sedimentation.The incompleteness of a section cannot give a precise chronostratigraphic correlation.It is suggested that holostratigraphy,based on high resolution event stratigraphy and global cyclostratigraphy and combined with biostratigraphy,magnetostratigraphy,chemostratigraphy and tectonic stratigraphy,be the mainstream of stratigraphy in the future.