Characteristics and Correlation of Coal Seams in the Yan'an Formation of the Southern Tianshuibao Coalfield at the Southwestern edge of Ordos Basin

To clarify the development characteristics, occurrence patterns and correlation reliability of coal seams in the Yan'an Formation of the southern Tianshuibao Minefield, at the Southwestern edge of Ordos Basin and support coal resource exploration and development, this paper systematically analyzes the structural framework, stratigraphic sequence, coal-bearing potential and spatial distribution of coal seams using regional geological data, borehole exploration data, logging curves, and coal petrology and quality test results. A multi-dimensional comprehensive coal seam correlation system centered on “coal-rock assemblage + marker beds + interlayer spacing + logging curves + coal petrology and quality characteristics” has been established. The results show that: (1) The Middle Jurassic Yan'an Formation is the only coal-bearing stratum in the area, which is divided into 4 lithologic members from bottom to top. A total of 10 coal seams (groups) and 32 coal splits have been developed, including 8 mineable and locally mineable coal seams. Among them, Nos.3 and No.5-2 seams are the major mineable coal seams, characterized by large thickness, good continuity and stable distribution; Nos.2-3 and 4 coal seams are subsidiary mineable seams; and Nos.7 to 10-1 coal seams are locally mineable. (2) The average total thickness of the Yan'an Formation is 312.74 m, with an average total coal seam thickness of 22.07 m (coal-bearing coefficient is 7.1%). The average total thickness of mineable coal seams is 13.47 m (mineable coal-bearing coefficient is 4.3%), indicating moderate coal-bearing potential and a relatively high degree of resource enrichment. (3) The B1 and B2 marker beds in the study area are widely distributed with distinct characteristics. Interlayer spacing differs significantly among coal seams, and logging curves such as natural gamma, apparent resistivity, and density show clear responses. Coal maceral composition, proximate analysis, ultimate analysis, and technological property indices exhibit high inter-seam discrimination. (4) Through comprehensive multi-method verification, the major mineable coal seams are reliably correlated, while the secondary and locally mineable coal seams are correlated with basic reliability, fully meeting the technical requirements of the exploration stage. The research results provide essential geological support for coal resource development planning, mine design, and resource reserve estimation in the coalfield.