Study on the Sedimentation Characteristics of Yacheng Formation in Changchang Depression, Qiongdongnan Basin

From the whole to local, based on the foraminifera and calcareous nannofossil data of the wells, lithology and tectonic paleogeomorphology, comprehensive analysis on sedimentary environment of Yacheng Formation in Qiongdongnan basin has been done. Thestudy results indicate that during the sedimentation period of Yacheng Formation, the northern part of this depression is continental at the early stage, in the middle and later stage, the fossil appeared discontinuously, being lagoon-tidal flat facies; the fos-sil appeared more continuously in the central depression in Qiongdongnan basin, the abundance and diversity are much higher, being deposited under restricted shallow-sea environment. Therefore, it is concluded that the environment of Changchang depression in this unit is restricted shallow-sea. Fan delta, delta, coastal plain and coastal marsh distribute around depression, large area of coast deposit are well developed in the slope, and shallow sea are well developed in the center of depression. According to the planar sediment filling characteristics and typical seismic profiles, combined with the previous study results, it is believed that Yacheng Formation in Changchang depression is typical graben sedimentation and developemt model.