Abstract: The deposition mechanism of fine-grained sediments is an important component of the source-to-sink system theory in fine-grained sedimentology. It is of great significance to reconstruct sedimentary environments, make clear the genesis of fine-grained sedimentary rocks, and predict the spatial distribution of unconventional oil and gas resources. To deepen understanding the fine-grained sedimentation processes, the paper analyzes the depositional mechanisms of fine-grained sediments. Through systematic review of previous research findings, it also comprehensively summarizes the influential factors, evolutionary process, and tectonic characteristics under diverse depositional modes. The results show as follows. (1)The depositional processes of fine-grained sediments are categorized into three fundamental types, i.e., mechanical deposition, chemical deposition, and biogenic deposition. (2)The mechanically deposited materials, including clay minerals, feldspathic minerals, and organic matters, can form sedimentary structures such as cross-bedding, wavy bedding, and lenticular bedding under the action of geological agents such as rivers, wind, bottom currents, and gravity flows. (3)The chemically deposited clay minerals, carbonate minerals, and organic matters can deposit as floccules, while organic matters can form complexes with clay minerals. The main controlling factors for chemical deposition are the species and concentrations of inorganic salts, pH levels, and hydrodynamic conditions in the aqueous system. (4)Biogenic deposition involves fine-grained sediments formed under the influence of biological activities, along with the carbonate minerals, siliceous minerals, and organic matters from skeletal remains, algae, and microbial mats. Climate and seasonal changes, volcanic eruptions, and hydrothermal activities are important factors controlling biogenic deposition. These findings provide scientific basis and technical support for clarifying the distribution characteristics of fine-grained sedimentary strata and predicting the distribution of unconventional oil and gas resources.

Key words: fine-grained sediment, deposition mechanism, depositional mode, mechanical deposition, chemical deposition, biological deposition, sedimentary characteristics

摘要： 细粒沉 积物沉积机理是细粒沉积学"源-汇"系统理论研究中的重要一环,对恢复沉积环境、理解细粒沉积岩成因和预测非常规油气资源分布等具有重要意义。为了深化对细粒沉积物沉积过程的理解,分析探讨细粒沉积物的沉积机理,通过对前人研究成果的系统梳理,总结归纳了对不同沉积方式的影响因素、形成过程、沉积构造特征等。研究结果表明:①细粒沉积物的沉积方式分为机械沉积、化学沉积和生物沉积3大类;②机械沉积的黏土矿物、长英质矿物和有机质等物质在河流、风、底流、重力流等地质营力作用下能够形成交错层理、波状层理和透镜状层理等沉积构造;③化学沉积的黏土矿物和碳酸盐矿物能够以絮凝体的形式沉积,有机质可以与黏土矿物形成复合体,化学沉积的控制因素主要是水体中的无机盐种类及浓度、水体的pH值和水动力条件等;④生物沉积包括生物活动影响的细粒沉积,以及来源于生物骨骼、藻类和微生物席的碳酸盐矿物、硅质矿物和有机质等,生物沉积的控制因素主要为气候、季节变化、火山喷发和热液活动等。研究结果可为明确细粒沉积地层的展布特征,预测非常规油气资源提供科学与理论依据。

关键词: 细粒沉积物, 沉积机理, 沉积方式, 机械沉积, 化学沉积, 生物沉积, 沉积特征