盐湖沉积物光释光测年研究:进展、挑战与展望

Optically stimulated luminescence chronology studies of salt lake sediments: progress, challenges and prospects

关键词:  盐湖沉积  光释光测年  蒸发岩矿物  年代学框架

Key words:  salt lake sediments  optically stimulated luminescence dating  evaporite minerals  chronological framework

摘要:

盐湖沉积是一种蕴藏着丰富矿产资源的特殊沉积。作为我国工农业生产所必需的战略矿产资源的主要沉积载体之一，盐湖的形成演化过程深刻影响着矿产资源的储量及规模。年代学是揭示盐湖沉积形成原因和演化过程的关键所在。文章在概述光释光 （OSL） 测年原理和盐湖沉积特征的基础上，系统梳理OSL测年法在盐湖沉积物（碎屑、蒸发盐、盐包裹体）定年中的研究进展，总结OSL测年在测定盐湖沉积时代中存在的挑战，展望该方法未来在盐湖沉积物定年中的应用潜力。

Abstract:

Background, aim, and scope Salt lake is a special deposit that contains abundant mineral resources. As one of the main sedimentary carriers of strategically essential mineral resources for industrial and agricultural production in China, the formation and evolution of salt lakes significantly impact the reserves and scale of mineral resources. Chronology is the key to uncovering the formation causes and evolutionary processes of salt lake sediment. This review aims to summarize recent advancements in luminescence chronology studies of salt lake sediments. Materials and methods Based on existing research findings, this paper systematically reviews the applications of optically stimulated luminescence (OSL) dating in different types of sediments within the salt lake sedimentary system. Results (1) Salt lake sediments are mainly composed of three types of basic particles: silicate detritus, evaporite crystals, and evaporite inclusion detritus. These sediments are characterized by diverse material compositions, variable groundwater flow fields, and complex geochemical systems. (2) Although the OSL dating method has been widely applied in dating loess, sand dunes, lacustrine deposits, and other sediment types, its application in dating salt lake sediments is still in the preliminary stage. (3) Theoretically, OSL dating can be used to establish a chronological framework for the sedimentary stratigraphy of salt lakes by using the three basic particles in salt lake sediments, namely, silicate detritus, evaporite crystals, and evaporite inclusion detritus, as materials. Discussion (1) In the process of OSL sample pretreatment for salt lake sediments, the pretreatment process for samples of evaporated salt grains and their inclusions remains immature. It is necessary to comprehensively consider and overcome the challenges presented by this type of samples, such as solubility, friability, multiple sets of cleavage surfaces, and a wide range of grain size variations, to prepare samples that meet the test requirements. (2) In the determination of the equivalent dose of salt lake sediment samples, halite crystal grains have the characteristics of rapid bleaching. Crystallization and recrystallization do not inherit the old signal. The signal is basically stable, the dose response is good, and the anomalous fading is basically stable on a long-time scale. These features endow it with great potential in dating the evaporite sedimentary layers in salt lakes. (3) During the determination of the annual dose rate of salt lake sediments, special characteristics such as diverse material composition, variable groundwater flow field, and complex geochemical system result in the complexity and difficulty of accurately measuring the annual dose rate. Conclusions Although OSL dating of salt lake sediments encounters numerous difficulties and challenges, particularly when it comes to the OSL dating of evaporite grains like halite, theoretically, it still holds significant potential to establish a reliable chronological framework for salt lake sediments and to uncover the mechanism of salt formation and mineralization of salt lake resources. Recommendations and perspectives As an extremely complex and special sedimentary unit, the chronological study of salt lake sediments holds great scientific significance in numerous disciplines, including paleoclimate and paleoenvironment, evaporite mineralogy, paleo-hydrogeology, and geomorphology. Future studies on OSL dating of salt lake sediments should focus on: (1) The establishment of a reliable pretreatment process for evaporite samples. (2) A more in-depth study of halite luminescence characteristics, as well as the establishment and proposal of new equivalent dose testing processes and technologies. (3) Comparative analysis in the complex depositional environment of salt lakes. This involves comprehensively leveraging the advantages and disadvantages of testing methods such as NAA, ICP-MS/OES, gamma spectrometry, alpha counter, and beta counter, and selecting an appropriate annual dose rate measurement method for salt lake sediments. The OSL dating method holds significant potential in dating salt lake sediments; however, it also confronts numerous challenges. The successful implementation of OSL dating in salt lake sediments will proactively advance research in multiple domains, including evaporite mineralogy, the geomorphologic evolution of arid zones, paleoclimate and paleoenvironmental alterations, and paleo-hydrological events.