Seismic characteristics of the Huaguang mass transport deposits in the Qiongdongnan Basin, South China Sea: Implications for regional tectonic activity

• Huaguang MTDs is a large-scale buried MTD system.
• Seismic data show many detail characteristic features of a large-scale MTDs.
• The MTDs gave some key information for tectonic activity in the northwestern SCS.
• The reversal of RRSZ may form the triggering mechanism of MTDs.

Mass transport deposits (MTDs) occur in the South China Sea region, within the Qiongdongnan Basin, north of Guangle Uplift and west of Xisha Uplift. The MTDs (termed the Huaguang MTDs) are widely distributed in the late Miocene sedimentary strata, which belong to the upper Huangliu Formation (8.2–5.5 Ma). Their general flow direction is from south to north. As a large-scale buried MTD system, it covers an area of more than 18,000 km2. The system must be closely related to regional tectonic events, climate change, and variations in sedimentation rate. The dominant period when the Huaguang MTDs developed corresponds to the phase when the Red River Shear Zone reversed from left- to right-lateral slip. This event may have a close relationship with local uplift of Indochina, volcanism, and fault activation or re-activation within the surrounding area. Later in the Miocene, the accelerated onshore denudation and offshore basin subsidence of eastern Vietnam, and development of a mountainous river system, led to filling of the Yinggehai Basin and rapid accumulation of sediment which formed the regional steep bathymetry and weak cementation within the sediments. The sediment characteristics provide the critical conditions for forming MTDs. Polygonal faults within the MTDs and underlying strata show that fluid leakage took place following deposition of the MTDs. We suggest that the dominant trigger mechanism for large-scale MTDs was the activation or re-activation of major faults and associated volcanism in the late Miocene.