巨型事件层综述^*

A review of megabeds

摘要

巨型事件层,简称巨型层(Megabed),在英文文献中广泛使用,但中文的正式出版物中尚未见报道。巨型层是指沉积物重力流所形成的巨型沉积层(单层厚度可达数十米至数百米,体积达数百立方千米),它们比周围正常沉积层的规模大1~2个数量级以上,在厚度、粒度、成分等方面与围岩常有明显差异,通常发育具有多层结构特征的垂向序列,记录了重力流流体转换、流体分异等搬运沉积过程,对于重大地质事件解析、盆地分析、物源/古地理恢复、地质灾害预防以及油气勘探等均有重要意义。本文首先系统厘定巨型层及相关术语的概念内涵,分析总结巨型层的沉积特征,包括其沉积规模、物质成分与结构序列,在此基础上探讨巨型层的识别标志、搬运沉积过程与触发机制,最后对目前存在的问题与未来研究方向进行探讨,旨在引起国内学者对巨型层的广泛关注和深入研究。

Abstract

Megabed is a widely used term in the English literature,but has not been reported in official Chinese publications. Megabeds refer to giant event beds formed by sediment gravity flows. They can reach tens of meters to hundreds of meters in thickness and hundreds of cubic kilometers in volume,that is,approximately 1-2orders of magnitude larger than their surrounding normal deepwater intervals. Megabeds tend to be distinct from enclosing strata in terms of their thickness,grain size,composition,and commonly show multi-layer vertical structures that may record gravity flow transformation,differentiation and other deepwater transport and depositional processes. They are of great significance to geological events and basin analysis,provenance/paleogeography restoration,geohazard mitigation,and oil and gas exploration. In this paper,the conceptual connotation of megabed and related terms is firstly reviewed,and then the sedimentary characteristics of megabeds are analyzed and summarized,including their scale,composition,vertical structure and sequence. On this basis,the transport and depositional processes,as well as the initiation mechanisms of megabeds are discussed. Finally,existing problems and future research directions are discussed. The aim is to arouse extensive attention and in-depth research on megabeds across China.

关键词

深水沉积 / 巨型层 / 巨型浊积岩 / 重力流 / 流体转换

Key words

deepwater sedimentation / megabed / megaturbidite / gravity flow / flow transformation

基金资助

*国家自然科学基金(编号: 41802132)、中国石油创新基金(编号: 2020D-5008-03)和中国石油重大科技专项(编号: 2023ZZ0201)联合资助