Seismic Characteristics and Distribution of Large Scale Mass Transport Deposits in the Qiongdongnan Basin, South China Sea

摘要

Large-scale mass-transport deposits (MTDs), here called the Huaguang MTDs, occur in the South China Sea region within the Qiongdongnan Basin, north of Guangle Uplift and west of Xisha Uplift. As a large-scale buried MTD system, the Guaguang MTDs cover an area of more than 18,000 km~2 and can be divided into four distinct sub-MTDs. Sediment sources for MTD1, MTD2 and MTD3 are from southern Guangle Uplift and eastern Xisha Uplift, and their transport directions are generally from south to north. However, the flow direction for MTD4, located in the northwest portion of the study area, is from west to east with a source in the Yinggehai Basin region. MTD1 and MTD4 merge to form two connected depocenters. Along their length, the MTDs are seen as continuous packages that extend to the northwest, with a maximum distance of ～ 180 km from Guangle Uplift. The maximum thickness of the deposits reaches ～950 ms two-way travel time. The Huaguang MTDs show prominent features characteristic of large landslides. The overall seismic fades includes highly disrupted reflectors, truncated reflectors, and steep side walls. The lateral margins are easily recognized on seismic profiles perpendicular to the flow direction as abrupt boundaries between the inner highly chaotic or weakly reflective seismic fades and the outer continuous undisturbed fades. The MTDs are widely distributed in the Late Miocene upper Huangliu Formation (8.3-5.5 Ma). The analysis of the Huaguang MTDs provides constraints for Late Miocene tectonic activity on the passive continental margin of the South China Sea.