Unconformity structural architecture and tectonic paleo-geographic environment: A case of the Middle Caledonian on the northern margin of Tibet Plateau and Tarim basin

The property and characteristic of structural architecture are differences between unconformity and unconformity surface. In this study,the 3-layer configurations of parallel unconformity,angular unconformity and heterolithic unconformity are analyzed, especially the structural deformation underlying unconformity surface,the distribution of the style of unconformity configuration in basin-wide,and the sequence architecture and initial sediments overlying unconformity surface. The unconformity configurations aredivided into 10 subdivision unconformities. The process of kinematic and dynamics during these unconformities formed are discussed. The distribution of unconformity configuration presents obviously differences between Silurian to Upper 0rdovician ( S/03 ) indifferent units of Tarim basin. The medium-low angle monocline and faulted-fold unconformity occurred on the upthrown blocks of a series of thrust faults with NEE-SWW trending at Tangguzibasi depression in the southern of Tarim basin. The low angle dipping-north monocline unconformity occurred widely from south and across the central uplift of basin to the southern of Awati-Manjiaerdepression,the parallel unconformity in the northwestern and the northeastern of Awati-Manjiaer depression,and locally low angle monocline and fold unconformity at the western and the eastern of the Tabei uplift in the northern of the basin. The analysis of balanced cross sections presents that there were the strongest shortening with SEE-NWW in southeastern of basin,and there existed the shortening with S-N orientation in the southern of basin before Silurian depositing yet. The unconformity configuration and fault system development responded to tecto-orogenic processes of the South Altun and the West Kunlun. Analyzing the sedimentary development and structure evolution,the tectonic paleo-geographic setting is reconstructed before Silurian depositing. The northern of Hetian paleo-uplift and the northwestern of NE-trending folds zone on Caledonian in Tangguzibasi depression should be favorable to the potential exploration area for the first large-scale period of hydrocarbon migration and accumulation.