Application of Growth Stratum Analyzing Method in Study the Formation Time of Reverse Structure-an Example of Leidong Sag in Beibuwan Basin

It is significant to infer the formation time of a reverse structure for oil and gas exploration in a hydrocarbon potential area. The reverse structures are well developed in Leidong Sag in Beibuwan Basin forms, being an anticline now, coexisting with growth strata. The growth strata, namely syn-tectonic sedimentary formation, deposited accompanying with the strata folding and deforma-tion. The growth stratum has a causal relationship with the formation of reverse structure and strata folding. Through analyzing the beginning time and the end time of the growth stratum, the formation time of reverse structure can be determinated. On the basis of the depositional angle and contact relationship, the development of growth strata in Leidong Sag can be divided into in three stages, of which the bottom of the Phase-1 growth strata corresponds to the bottom boundary of the Upper Oligocene, and the top of the Phase-3 growth strata corresponds to the top boundary of the Upper Oligocene. Therefore, it can be concluded that the reverse struc-ture formed in Late Oligocene, and developed during three stages due to the intermittence of tectonic activity.