Characteristics and main controlling factors of the shelf-edge delta of the lower member of Zhujiang Formation in the northern Baiyun Depression

In order to reveal the evolutionary history and controlling factors of the shelf-edge delta discovered in the Lower Member of Zhujiang Formation in the northern Baiyun Depression, seismic sedimentology and sequence stratigraphy are applied with the support of drilling data, logging data, seismic reflection configuration and root mean square amplitude attributes. Seismic reflection characteristics suggest a high angle oblique progradational body in parallel to the direction of sediment movement. Topset deposits are missing. Instead there are fan deposits in front of the delta laid on the bottom of the basin. The vertical sequence of the delta is characterized by the multiple reverse cycles changing from prodelta, sheet sand, mouth bar to underwater distributary channel upwards. There are abundant bioturbated structures, shale strip deformation and sliding features usually found on continental slope. The shelf-edge delta in the Lower Member of the Zhujiang Formation was formed in forced regressive systems tract periods, and accompanied by basin floor fans. However, in the lowstand system tract period there were mainly developed slope fans and low wedgelike sand bodies. A stable distribution of shelf break zone was formed in the period while the Lower Member of Zhujiang Formation was deposited under the control of tectonic movement. Shelf-edge delta occurred in the shelf margin and slope area by the huge amount of sediment discharge from the paleo-Pearl River and the strong sea-level falling then.