Research progress on discriminating sedimentary environments using geochemical indicators of coal and coalbed methane

To accurately reconstruct the sedimentary environment during the coal-forming period and support coal resource evaluation as well as coalbed methane （CBM） exploration and development, this paper systematically reviews the research progress on discriminating sedimentary environments using geochemical indicators of coal and CBM, while focusing on constructing and expounding the environmental indication mechanisms of four categories of core indicators: among them, for trace elements, Boron （B） content and Sr/Ba ratio are used to characterize salinity, V/Cr and V/（V+Ni） ratios are applied to distinguish redox conditions, and sulfur （S） element reflects the properties of water bodies; rare earth elements （REEs） employ total REE content and Eu/Ce anomalies to reveal provenance and paleoenvironment; stable isotopes, specifically stable carbon （C）, hydrogen （H）, and oxygen （O） isotopes, can indicate gas genesis and paleovegetation; and biomarkers refer to biomolecules such as n-alkanes and terpenoids that are capable of tracing coal-forming vegetation and redox environments. Meanwhile, this paper compares and analyzes the research characteristics of this field at home and abroad. A prominent feature of domestic research is the integration of geochemical indicators with regional tectonic evolution, with emphasis on interdisciplinary collaboration. In contrast, foreign research focuses more on the study of micro-mechanisms and the construction of quantitative models, and extensively applies molecular organic geochemistry methods. Current research still faces challenges, including the multi-solution nature of indicators, interference from secondary transformation, and insufficient research on deep coal seams with a burial depth ＞2 000 m. In the future, it is necessary to establish a “element-isotope-molecule” multi-indicator coupling model, strengthen geochemical research and technological innovation on deep CBM, so as to provide more reliable theoretical support for resource exploration and paleoenvironment reconstruction.