Distribution characteristics and genesis of unconformity surfaces from Late Ordovician to Jurassic in Tarim Basin

The study of unconformity holds significant guiding importance for basin evolution, paleogeomorphology reconstruction, and oil and gas exploration. Affected by multiple tectonic activities, various types of unconformities have developed in the Tarim Basin. Through the analysis of seismic profile data, the distribution and structural characteristics of the unconformity surfaces formed during the Late Ordovician to Jurassic period in the Tarim basin are studied, and their tectonic mechanisms are discussed. The results show that: (1) The types of unconformity structures in the Tarim Basin are mainly parallel, truncation, fold, fault-fold, superimposed-overlap, single-overlap, and heterogeneous unconformity. (2) The bottom boundary of the Silurian exhibits the development of fault-fold, fold, truncation, superimposed-overlap, single-overlap, and parallel unconformity, distributed in an east-west belt. There is a development of a wide range of angular unconformity in the middle and south of the basin, a development of parallel unconformity in the middle and north of the Awati-Mangar depression, and a development of a small range of angular unconformity in the Tabei uplift.The Devonian-Carboniferous bottom boundary exhibits the development of parallel, truncation, fault-fold, single-overlap, superimposed-overlap, and heterogeneous unconformity, and the plane distribution has the characteristics of north-south symmetry with the axis of the connection of sedimentary centers in the Northern depression. The bottom boundary unconformity of the Triassic exhibits the development of superimposed-overlap unconformity, low-angle truncation unconformity, and parallel unconformity from north to south, reflecting the closed orogenic movement of the southern Tianshan Ocean in the northern margin of the basin in the late Hercynian. A development of fold, truncation, superimposed overlap, and heterogeneous unconformity exhibits in the bottom boundary of the Jurassic, with the axis-like symmetrical distribution of the sedimentary center line in the Manjiaer-Yingjisu depression. (3) The distribution characteristics of the unconformity surfaces reflect the differences in tectonic movements, the migration and activity of paleouplifts, and the controlling role of unconformity on hydrocarbon accumulation in the basin.