Jiralangtu Depression is located at the southwestern part of the Wunit subbasin

Erlian Basin. It is a NE-trending half-graben with a fault belt in the north side and an overlap in the south side. The depression subsided in the early stage and uplifted in the late stage. Two kinds of genetic heavy oils could be found within the depression such as primary heavy oil and biodegraded heavy oil. Each of them has its own formative mechanism and geochemical features. Geochemical analysis of the crude oils shows that the heavy oil pools distributed along the southwestern slope of the Jirgalangtu Depression contain slightly-intermediately biodegraded immature heavy oils.