Identification of Mass Transport Deposits and Insights into Gas Hydrate Accumulation in the Qiongdongnan Sea Area, Northern South China Sea

Abstract

Accurately identifying the Bottom Simulating Reflector (BSR) is a crucial and fundamental task in seismic exploration and the interpretation of gas hydrates in marine areas. During our seismic interpretation and inference work on a gas hydrate survey in the Qiongdongnan Sea area, we encountered a phenomenon that closely resembled the seismic reflection characteristics of BSR. By comparing and identifying various geological phenomena, we have determined that this unique seismic reflection phenomenon is, in fact, the reflection of the depositional bottom interface known as “mass transport deposits (MTDs)” as described by previous researchers. The physical properties of the MTDs developed on the shallow surface of the seafloor are similar to those of gas hydrate reservoirs in the seismic exploration of marine areas, particularly in the northern South China Sea’s Qiongdongnan Sea area. Due to the lack of active neotectonic movement in the area, most identified BSR reflection occurrences are parallel to the seafloor. Consequently, during the process of seismic interpretation of BSR in the Qiongdongnan Sea area, it may be confused with the bottom boundary reflection interface of MTDs. Accurately identifying MTDs’ sedimentary bodies in gas hydrate exploration activities in this area would greatly enhance the accurate identification of BSR and support the refined evaluation of gas hydrate resources. In this paper, the structural characteristics of MTDs are compared with the reflection characteristics of seismic profiles, the reflectors are identified as MTDs rather than BSR through analysis and interpretation, and the possible mechanism of hydrate accumulation in this region is discussed.