关键词: 珠江口盆地, 恩平凹陷, 串沟河道, 沉积模式, 岩性圈闭

Abstract: Chute channel is an important depositional unit in the development of fluvial systems, but there are few systematic studies focusing on its sedimentary characteristics and processes. In this paper, a series of typical chute channel deposits have been identified in the lowstand systems tracts of the sixth member of the Hanjiang Formation in the northern Enping Sag using cores, well logs and 3D seismic data. On seismic profiles, chute channels are generally isolated high-amplitude anomalies. Seismic attributes and slices from frequency decomposition and RGB blending indicate that chute channels are general straight and widen from NE to SW. They gradually pinch out to the NE direction. Core data shows that the lithology of chute channels is mainly gravel bearing coarse sandstones. Compared with the existing models and modern examples, the chute channels developed in the northern Enping Sag is so unique that it is located in a background of mud-rich flood plain rather than braided bars. Based on the comprehensive analysis of the sedimentary processes, it is proposed that the chute channels within the study follow the upstream expansion model: episodic flooding can influence preexisted flood plain between the braided channels, triggering the headward erosion of the chute channels from the low-lying area downstream of the flood plain. Generally, the chute channels have good physical properties and can be further buried by transgressive mudstones, thus having excellent lateral and top sealing conditions. Consequently, chutes channels may form an important lithologic trap type within the whole basin. The finding of this study can provide new enlightenment for the exploration of lithologic traps in the Pearl River Mouth Basin.

Key words: Pearl River Mouth Basin, Enping Sag, Chute channel, depositional model, lithologic trap