The evolution of the slope breaks in Qiongdongnan Basin and their controlling factors

摘要

Qiongdongnan Basin (QB) experienced three main tectonic stages in the Cenozoic: rifting, thermal subsidence, and accelerated subsidence. Corresponding to these stages, the slope breaks also underwent three different evolutionary stages, which differed in space and time between the east and west of QB. Structural slope breaks developed during the rifting stage in the Paleocene. Transitional sedimentary strata without obvious slope break developed in the neritic environment during the thermal subsidence stage in the Neocene. Sedimentary slope breaks and gentle slope zone without slope break developed during the accelerated subsidence stage. The sedimentary slope breaks could be further classified into progradational and aggradational types, the starting points of which varied in space and time. Spatially, the progradational sequences in the Ledong and Lingshui sags started at the north of today's deep central basin, distant from the basin edge. In the Songnan and Baodao sags, the aggradational sequences were close to the sag edge and essentially controlled by the underlying major boundary faults. Temporally, sedimentary slope breaks developed early in the east and late in the west and were initially partitioned and eventually unified. Fault activity controlled the types and ending time of structural slope breaks during the rifting stage, while tectonic subsidence controlled the time and places of progradational slope breaks during the accelerated subsidence stage. Sediment supply controlled the superposition patterns of the sedimentary sequences of the sedimentary slope breaks. It is suggested that the evolutionary history of the slope breaks has been primarily affected by the southward transition of the South China Sea ocean ridge, the westward collision of the Philippine Sea Plate, and the dextral strike-slipping of the Red River Fault.