Sedimentary evolution characteristics of Paleogene Wenchang Formation in eastern Baiyun Sag, Pearl River Mouth Basin

Key words:  sedimentary facies  sedimentary model  Wenchang Formation  Baiyun Sag  Pearl River Mouth Basin

Abstract:

This study extensively utilizes new 3D seismic data in conjunction with well log and logging data to investigate the sequence stratigraphy, sedimentary characteristics, and sedimentary evolution of the Wenchang Formation in the Paleogene of Baiyun Sag in the Pearl River Mouth Basin. Additionally, it aims to re-establish the sedimentary system evolution process within the third-order sequence framework of the Wenchang Formation. The results reveal that the Wenchang Formation in the eastern Baiyun Sag can be divided into five third-order sequences from bottom to top, corresponding to three tectonic evolution stages:the initial rifting period (WCSQ1), early detachment rifting period (WCSQ2, WCSQ3) and late detachment rifting period (WCSQ4, WCSQ5). During the initial rifting period, several isolated half-grabens were present, characterized by braided river deltas with axial source in gentle slope, near-source fan deltas in steep slope, and shore-shallow lacustrine sediments. During the early stage of the detachment rifting period, intense faulting activity led to the rapid expansion of the lacustrine basin. Semi-deep lacustrine facies developed in a limited manner, the depositional center shifted northward, and the large braided river delta deposition occurred in the Panyu low uplift in the north. As the late stage of detachment rifting period, fault activity weakened, and the lacustrine basin gradually contracted. The depositional center stabilized in the middle of Baiyun Sag, with the predominant development of small braided river delta deposition and shore-shallow lacustrine facies. Notably, large braided river delta and fan delta sand bodies are identified as favorable reservoirs in the eastern Baiyun Sag.