Fault-controlled contourite drifts in the southern South China Sea: Tectonic, oceanographic, and conceptual implications

Abstract

Over the past decades, contourite drifts have been widely identified in the deep ocean with their classification constantly being improved. Some contourite drift types, however, are not yet well constrained. The present study investigates contourite drifts in the southern South China Sea for the first time based on high-resolution reflection seismic profiles and bathymetric data, thereby determining the common occurrence of a lesser-known type: the “fault-controlled drift.” In this area, normal fault movements have been active during the Quaternary, associated with the formation of sea-floor irregularities and highs that represented obstacles to Deep Water circulation. Six fault-controlled drifts are generated in the study area due to interactions between regional faulting/fault-generated topography and bottom currents. They are divided into two major types depending on their shapes, locations, and relative faulting movements: Type-1) drifts deposited coeval to the fault movement and are situated over the footwall block top or along the fault scarp, and Type-2) drifts deposited after the fault movement and are located along the fault scarp base. Spatial distribution of these drifts is a result of variations on bottom currents dynamics associated with the South China Sea Deep Water. The South China Sea Deep Water settling depth, 200–300 m shallower than that of the northern South China Sea, tentatively indicates upwelling which may have, in turn, contributed to the South China Sea meridional overturning circulation. The present study demonstrates new types of contourite drifts that are not well-constrained in the literature and require more detailed studies. The types of fault-controlled drift are described based on the relative movement of normal faults. However, future research should be conducted in other active tectonic settings for evaluating fault effects on the sedimentary stacking patterns, geometries, and evolution of contourite drifts.