关键词: 珠江口盆地, 白云凹陷, 古近系, 物源体系, 时空演化

Abstract:  Baiyun sag is located in southern Pearl River Mouth basin, which is an inherited deep sag. The current exploration results show that it is a gas-rich sag. However, it is controlled by the paleogeomorphology pattern, fault combination, source supply, and paleo-valley-slope break system of the Paleogene Wenchang Formation and Enping Formation in Baiyun sag. There are many different types of source-sink systems in the study area. In this paper, through detailed rock mineralogical analysis and three-dimensional seismic data, the coupling and time-space evolution of the Paleogene source-sink system in Baiyun sag are revealed. In the early stage of rifting (Lower Wenchang Formation), the source was dominated by Mesozoic intermediate-acid igneous rocks in the basement of the basin. The basin as a whole showed a pattern of depression and uplift. The sedimentary center and deep sag were controlled by two groups of axial faults trough sources with different distribution directions in NWW and NE directions, and formed felsic-rich sand bodies. The distribution range of sand bodies in this period is very limited, mainly showing the characteristics of short range and low structural maturity. The axial provenance of the Upper Wenchang Formation gradually shrank, and the scale of the northern provenance channel restricted by the gully system gradually increased. Compared with the Lower Wenchang Formation, the clastic rocks of the Upper Wenchang Formation had higher structural maturity and compositional maturity, showing a large-scale transportation process. The lithofacies paleogeography and provenance system pattern of the Eenping period are obviously different from those of the Wenchang period. It is characterized by the typical sedimentary characteristics of shallow water and wide basin, and large-scale shore-shallow lacustrine facies and braided river delta are developed on the side of the northwest channel. The scale of the source area in the basin is significantly reduced, and the long axis source system outside the basin restricts the distribution of large-scale sand bodies.

Key words: Pearl River Mouth basin, Baiyun sag, Paleogene, provenance system, spatiotemporal evolution