Cenozoic architecture and structural development of the eastern Qaidam basin

This study aims to reveal Cenozoic architecture and structural development of the eastern Qaidam basin. Seismic profiles show that Cenozoic strata become thinner and pinch out toward the northern and southern edges of the basin, and the northern basin has been greatly modified by the Oulongbulukshan and Aimunikshan uplifts. Based on the analysis of lateral variations of Cenozoic strata and stratigraphic sections, it is demonstrated that the Oubei fault initiated in the Late Miocene, leading to rising of the Oulongbulukshan uplift and formation of the Delingha depression. The Aibei fault became active in the Pliocene, and north-directed thrusting of both the Aibei and Oubei faults resulted in further subsidence of the Delingha depression and deposition of the Shizigou Formation up to 2600 m thick. The Quaternary witnessed large-scale thrusting of the Ai'nan fault, which not only caused uplifting and southerly displacement of the Oulongbuluk mountain and Aimunik mountain on the north but also the generation of the Hobuxun depression on the south. The Hobuxun depression then became the depocenter of the eastern Qaidam basin. Previous basin models, such as foreland basin or piggyback basin models, apparently failed to interpret both the Cenozoic architecture and structural development of the eastern Qaidam basin. It is proposed that the eastern Qaidam basin was formed as a result of crustal folding related to strong horizontal compression, i.e., the eastern Qaidam basin was a crustal-scale synclinal basin. The synclinal basin model can well account for the thinning of strata toward basin margins and localization of depocenters in the middle of the basin during the Cenozoic. Reconstruction of structural evolution of the eastern Qaidam basin will help understand lateral growth of the northeastern Tibetan plateau.