Abstract:

Kailu Region in the south part of the Songliao Basin is a Meso-Cenozoic sedimentary province that covers an area of 3.2×10⁴km² and developed the Upper Jurassic Series,Cretaceous and part of Tertiary Systems. The sediments that overlaid on Proterozoic-Paleozoic metamorphic basement reached the maximum thickness of 4500m. Kailu Region underwent four tectonic evolution stages that are tensional faulting, fault-subsiding,depressing and compresson-shearing, and can be divided into 5 first order tectonic units and 14 secondary tectonic units. A series of elongated contemporaneous normal faults that stretches NNE or NW with big vertical throws and a group of separate graben-like lake basins in which igneous rocks developed in the early stage and shore-shallow lake sediments in the late stage formed in the Jurassic due to the underthrusting of the Pacific Plate and the updoming of mantle.Faulting basically stopped in the Early Cretaceous and the whole region subsided under isostutic effect, resulting in stable extensive shore-shallow lake deposits. From Late Cretaceous to Tertiary, the variation of regional stress field caused horizontal compression on the southeast margin, thus forming northeast trend surface folds and causing particular normal faults to reversal. There are thick dark mudstones in the Jurassic (occupying 60-90% of the total thickness), which has rich organi matter (organic carbon 2-3% ), type-Ⅰ and type-Ⅱ of kerogen and widespread oil-gas shows. The threshold depth for oil generation is 1300m. It is considered that the Jiufotang and Shahai Formations are the main oilgenerating intervals, and the Lujiabao Depression, Bao'an and Naimanqi Sags in the Zhezhong Depression are the most prospective regions for hydrocarbon exploration.