Integrated well-seismic analysis of sedimentary facies distribution: A case study from the Mesoproterozoic, Ordos Basin, China

To advance the understanding of Mesoproterozoic sedimentary facies and delineate their distribution patterns in the Ordos Basin, this study systematically analyzes the sedimentary characteristics and stratigraphic architecture of the Mesoproterozoic sequences using integrated datasets, including core samples, well logs, seismic profiles, and field outcrops. The results indicate that the Mesoproterozoic Changcheng System, shaped by rift-related processes, displays a southwest-to-northeast thinning trend, culminating in stratigraphic pinch-out. Three Facies associations are identified: rift-related sandstone-shale and volcanic eruption facies (dominated by sandstones with abundant basaltic eruptives in the Changcheng rift trough), shoreface sandstone facies (primarily lower shoreface subfacies with quartz sandstones and mudstones), and fluvial facies (sandstone-siltstone sequences). During the Jixian System, post-Changcheng “compensatory sedimentation” led to a significantly reduced depositional area dominated by tidal flat environments. A southwest-to-northeast facies transition progresses from shelf facies (siltstones interbedded with shales and bioclastic limestones) through mid-ramp facies to tidal flat and mixed tidal flat facies, collectively forming a carbonate tidal flat system dominated by siliceous-banded dolomites. The Mesoproterozoic succession in the Ordos Basin thus records an evolutionary trajectory from rift basin infilling (“leveling”) to the development of a shallow marine clastic-carbonate platform during the Jixian System, reflecting progressive tectonic stabilization and paleoenvironmental transitions.