Establishment of an astronomical time scale for the Shizigou Formation in the Qaidam Basin, Inner Asia and orbital forced evolution of lakes during The Pliocene

Abstract

The Qaidam Basin, as the largest inland basin within the Tibetan Plateau, has accumulated more than 10,000 m of Cenozoic continental sediments. It serves as a crucial research area for documenting Cenozoic climate changes and plateau uplift processes in the Asian interior. Additionally, the basin holds vast reserves of oil and gas resources, making high-resolution drilling data invaluable for studying paleoclimate. In this study, the long-sequence lacustrine deposits of JS1 drill core across the Shizigou Formation in the Yiliping Depression at the western center of the basin were studied, aiming to establish an astronomical timescale for the Shizigou Formation and investigate the characteristics of paleoclimatic changes during the late Miocene to the Pliocene for the Asian interior. The analysis was carried out using high-resolution natural gamma ray (GR) data sequences, employing techniques such as spectral analysis, filtering, and wavelet analysis in cyclostratigraphy. The results indicated the presence of a stable Milankovitch orbital signal was perfectly recorded in the Shizigou Formation, primarily influenced by eccentricity cycles, with weaker obliquity and precession cycles. Using the stable and continuous 405 ka eccentricity cycle in astronomical tuning, a "floating" astronomical timescale with a duration of 6.1 Ma for the Yiliping depression's Shizigou Formation has been established. With reference to previously established stratigraphic age anchor points, an absolute astronomical timescale (2.5–8.6 Ma) has been ultimately provided for the Shizigou Formation. Simultaneously, a clear 100 ka short eccentricity cycle record has been identified during the Pliocene (5.3–2.5 Ma), which corresponds in time with the aridification within the basin during this Pliocene period. In addition, a comparison of the Pliocene natural gamma ray curve of the Qaidam Basin with global ice volume variations indicated that the basin's aridification was influenced by global cooling, with eccentricity-modulated precession cycles controlling solar radiation and subsequently affecting the evolution of lakes in the arid region of Inner Asia.