Sedimentary characteristic and evolution of Late Oligocene to Early Miocene in Baiyun depression, Pearl River mouth basin

Based on the studies of cores, well logs, seismic and paleontology data of Baiyun depression in Pearl River mouth basin, combined with previous research results, the paper synthetically analyzed the characteristics of sedimentary facies and evolution of sedimentary filling from Late Oligocene to Early Miocene in the depression. The results show that shallow delta deposition developed in Lower Zhuhai Formation, seismic reflection characteristics show that the delta has three phases, microfacies of underwater branching channel, inter-tributary bar,river mouth bar, distal bar were drilled, characterized by sand-rich sediments, washing-filling structure, graded bedding, thick horizontal burrows and other structures were developed. The upper of Zhuhai Formation was of neritic facies, characterized mainly by marine interbedded sandstone and mudstone.At that time the shelf slope-break zone was located on the southern slope of Baiyun depression. The eustatic cycles of sea level were frequent and the shelf slope-break zone moved to the northern slope of Baiyun depression during deposition of Zhujiang Formation. As the expansion of the ancient Pearl River, the input of sediment increased and a deep-water fan sedimentary system developed in Lower Zhujiang Formation. Sediments consisted mainly of fine sandstone to coarse sandstone, with a small quantity of siltstone and deep-sea mudstone. Four major gravity flows developed, including particle flow, liquid flow, turbidity flow and debris flow. Channel deposits of inner fan, deposits of abandoned channel of middle fan, overflow deposits between the channels and deep-sea sediments outside fan were drilled. The Upper Zhujiang Formation was of bathyal facies with abyssal mudstone as major sediments.