This paper is the result of geothermal geological survey engineering.

Objective Erlian Basin is one of the important petroliferous basins in China. Baibei Sag is one of the important petroliferous basins in Erlian Basin with exploration and development value. It develops many source rock intervals such as Tengger Formation and Aershan Formation. Exploring the tectonic thermal evolution history of Baibei Sag in Erlian Basin is of great significance for the exploration and development of fossil energy in Baibei Sag.

Methods According to seismic and logging data, combined with temperature measurement data, the erosion thickness of Saihantala Formation and Erliandabusu Formation is restored by using mudstone acoustic time difference method and vitrinite reflectance method, and then the burial history and tectonic thermal evolution history of Baibei Sag in Erlian Basin since Cretaceous are restored.

Results The results indicate that Baibei Sag in Erlian Basin exhibits structural development characteristics of "differential subsidence in the early stage, uniform subsidence on a large scale in the middle stage, and overall uplift and erosion in the late stage". At well S1, during the deposition period from Aershan Formation to Saihantala Formation, the study area subsided rapidly. After reaching the maximum burial depth at the end of deposition, the first stage of uplift and erosion occurred, with erosion amount of about 1314 m. During the deposition period from Saihantala Formation to Erliandabusu Formation, rapid subsidence occurred again, and then the second stage of uplift and erosion occurred, with erosion amount of about 170 m. Since Paleogene, the sag has been in a stable subsidence stage, depositing 100 m of Cenozoic strata. At the end of the early Cretaceous, the average geothermal gradient at the maximum burial depth was 3.65℃/100 m, which was in a state of thermal anomaly, and then gradually decreased to the current geothermal gradient of 2.94℃/100 m, with a geothermal flow value of 58.8 mW/m².

Conclusions The maturity of source rocks is controlled by paleotemperature and burial depth, reaching the maximum degree of thermal evolution at about 77 Ma (Tengger Formation: 0.50%<R_o<0.68%; Aershan Formation: 0.72%<R_o<0.76%). However, Duhongmu Formation and Saihantala Formation are in an immature stage and have almost no hydrocarbon generation potential. It is of great significance to study the characteristics of paleo−modern geothermal field in Erlian Basin and provide theoretical support for oil and gas exploration in the study area.