Seismic characteristics and distributions of Quaternary mass transport deposits in the Qiongdongnan Basin, northern South China Sea

摘要

Mass transport deposits can cause marine geohazards and transport sediments to deep-water areas and act as hydrocarbon reservoirs and seals, which have been extensively examined throughout the last decade in the northern South China Sea. Based on 2D and newly acquired high-resolution 3D seismic data, as well as logging-while-drilling (LWD) data, we document the characteristics, distributions, sources, and triggering mechanisms of the Quaternary MTDs in the Qiongdongnan Basin (QDNB). Moreover, their impacts on deep-water channels, gas hydrate accumulation and marine geohazards are discussed. The results show that there are ten phases of Quaternary MTDs development in the study area. Among them, MTD3 covers the largest area, ～627 km~2, while the smallest is MTD10 at ～89 km~2. These MTDs are characterized by chaotic and translucent/transparent seismic facies and negative-phased seismic reflections on their seismic profiles. The transport directions of these MTDs mainly occur from the northwest to southeast, northeast to southwest, and southwest to northeast, with sources in the Northern Slope Area and Western Slope Area or Guangle Uplift Area. Based on an analysis of the tectono-sedimentary evolution of the QDNB, these Quaternary MTDs may have been triggered by an anomalously high sedimentation rate, increased slope gradient, fault reactivation, earthquakes, and sea level fluctuation. Among these processes, earthquakes and rapid sea level fluctuation could be the most critical triggering mechanisms. Furthermore, the MTDs primarily act as hydrocarbon seals in the study area, facilitating the accumulation in the shallow gas reservoirs and gas hydrates within the Quaternary strata. MTDs and related tsunamis are also major marine geohazards, which need in-depth integrated researches by multidisciplinary scientists.