Recurrent slope failure enhancing source rock burial depth and seal unit competence in the Pearl River Mouth Basin, offshore South China Sea

Abstract

High-quality 3-D seismic data are used to assess the significance of mass-transport deposits (MTDs) to the evolution of the Pearl River Mouth Basin (South China Sea). Basal shear surfaces and lateral margins of seven recurrent MTDs are mapped to reveal a general NE-SW transport direction throughout the Late Miocene-Quaternary. A key result of our analysis is the perceived relationship between the recurrence of slope instability in the study area and the Dongsha Tectonic Event. Using borehole data to constrain the ages of interpreted MTDs, we show that tectonic uplift in the northern South China Sea led to slope oversteepening in the Late Miocene (between 10.5Ma and 5.5Ma), preconditioning it to fail recurrently for more than10Ma. Interpreted MTDs are shown to enhance burial depths of source and reservoir units, and improve seal competence in lower-slope areas. Conversely, upper slope regions record important erosion and reduced sealing capacity in Late Cenozoic strata. As a result, we postulate that the thickness variations imposed by MTDs on Late Miocene-Quaternary strata have important implications to petroleum plays in the South China Sea.