The Sequence Stratigraphy of Mixed Carbonate-Siliciclastic Depositional Systems in the Northern South China Sea

The mixed carbonate-siliciclastic deposition is very popular in Neogene in the northern South China Sea(SCS). The paleo-Zhujiang delta facies is main petroleum reservoir of the Zhujiangkou Basin. The other reservoir is carbonate reef.

The paleo-topography, sedimentation and strata superimposition styles in the mixed carbonate-siliciclastic deposition in marine shelf of the northern SCS show the following characteristics: (1) The paleo-topography gradients of the sequence boundaries such as SB18SB17.5,SB17 and SB16.5 are 4.7, 0.38, 0.17 and 0.13 degrees, respectively; (2)The siliciclastic sediments within the sequences such as NSQ2 (21 to 18Ma), NSQ3(18 to 17.5Ma), NSQ4(17.5 to 17.1Ma) and NSQ5(17.1 to 16.5Ma) were deposited in relatively paleo-topographically low area; in contrast, the carbonate deposition occurred at high paleo-topographic area.
(3)In four sequences of NSQ2(21 to 18Ma), NSQ3(18 to 17.5Ma), NSQ4(17.5 to 17.1Ma) and NSQ5(17.1 to 16.5Ma), the carbonate sediments were overlain by the siliciclastic sediments in paleo-topographically lower area, while the carbonate was overlain by the sequence bourdaries in paleo-topographically higher area of Dongsha uplifted area.

The relative sea level change, sediment supply and paleogeography may have been the main controlling factors of the level 3 sequence based on the following analysis of the sequence characteristics. In the northern shelf of SCS, the siliciclastic sediments were deposited during the period when relative sea level fall rapidly and rose slowly. In contrast, the carbonate sedimentation, such as biogenic reef, occurred during the rapid rise in relative sea level and early highstand system tract. Because of the pulsation of sediment supply of paleo-Zhujiang River, the distribution patterns of deposits are various in different stratigraphic sequences. Siliciclastic sediments were deposited from abundant terrigenous siliciclastic sediment supply system. In contrast, the carbonate deposits occurred from “clean water” conditions. The original palae-geomorphy also exerted a significant influence on the styles of stratigraphic sequences. For example, during HST of NSQ2, the wide shelf area of Huizhou was paleo-topographically flat and thus no significant supply of siliciclastic sediments, consequently, the limestone reefs and beaches developed. The carbonate deposition resulted in the sediment shelf-break in the wide shelf area of Huizhou and the unconformity contact between sequences.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California