Precise stratigraphic framework of the Bashijiqike Formation of Cretaceous in the northern Kuqa Depression, Tarim Basin and its geological significance

Introduction The Bashijiqike Formation in the northern Kuqa Depression of the Tarim Basin is critical for Cretaceous petroleum exploration, yet its high-resolution stratigraphic framework remains poorly constrained. This study aims to construct a precise stratigraphic framework of the Bashijiqike Formation and reveal the coupling relationship between astronomical orbital cycles and hierarchical sequence boundaries. Methods Integrating field outcrop observations and well-logging data, this work applies high-resolution sequence stratigraphy and cyclostratigraphic principles. Gamma-ray (GR) logging series and outcrop datasets are adopted to carry out hierarchical sequence division and cyclostratigraphic analysis. Results The Bashijiqike Formation is subdivided into 3 third-order sequences, 7 fourth-order sequences, and 28–31 fifth-order sequences. Spectral filtering of the GR time series demonstrates robust coupling between sedimentary astronomical signals and sequence stratigraphic hierarchies. The ~1.2 Myr obliquity cycle corresponds to third-order sequences, the 405 kyr long eccentricity cycle matches fourth-order sequences, and the 131 kyr short eccentricity cycle is linked to fifth-order sequences. Moreover, the 40 kyr short obliquity cycle correlates with individual sand beds, whereas the 20 kyr precession cycle corresponds to interbeds. Conclusions The cyclostratigraphy-based high-precision stratigraphic workflow established herein provides a reliable approach for identifying single sand beds and interbeds, with important implications for fine-scale reservoir characterization of the Bashijiqike Formation.