镁同位素示踪生物扰动灰岩的选择性白云石化过程

在碳酸盐岩沉积环境中，生物扰动作用会导致选择性白云石化作用的发生，表现为生物潜穴充填物发生白云石化而围岩不发生白云石化。目前对生物扰动灰岩选择性白云石化过程的控制因素及具体机制尚缺乏系统研究。鉴于镁同位素在示踪白云岩镁来源及白云石化过程中的独特优势，本申请提出以镁同位素为核心研究手段，对华北地台奥陶系马家沟组生物扰动灰岩的选择性白云石化过程进行半定量-定量模拟，并在沉积学-岩石学研究的基础上，辅以碳、氧同位素和微量元素地球化学分析，对生物扰动灰岩的选择性白云石化过程进行综合研究，明确生物扰动作用对选择性白云石化过程的控制机制，厘清选择性白云石化作用发生的时间、镁离子来源及运移方式，进而建立生物扰动灰岩的选择性白云石化模式。本项研究将进一步拓展镁同位素在白云岩成因研究中的应用，对推动关于“白云岩问题”的理论创新具有重要意义。

In certain cases, dolomite distribution clearly indicates selectivity with respect to primary fabrics and textural properties on macroscopic or microscopic scale. One type of fabric-selective dolomitization, characterized by dolomitic burrows and micrite matrix, is recognizable in bioturbated limestone from the Ordovician Majiagou Formation, North China. Although occurrences of dolomitized burrows within the rock record are common, the cause and process of selective dolomitization associated with the burrows can be difficult to determine. Considering the advantages of Mg isotopes in tracing Mg sources and dolomitization processes, we propose to use Mg isotopes to quantitatively or semi-quantitatively simulate the dolomitization process, coupled with carbon, oxygen isotopes and trace elements analyses to explore the selective dolomitization process of the bioturbated limestone in the Majiagou Formation. This study, aiming at clarifying the mechanism of selective dolomitization controlled by bioturbation, and establishing the selective dolomitization model of bioturbated limestone, will further expand the application of magnesium isotopes in the study of dolomite and promote the theoretical understanding of the “dolomite problem”.