Sequence architecture and depositional evolution of the northern continental slope of the South China Sea: responses to tectonic processes and changes in sea level

Abstract

The continental slopes of the South China Sea (SCS), the largest marginal sea on the continental shelf of Southeast Asia, are among the most significant shelf-margin basins in the world because of their abundant petroleum resources and a developmental history related to sea floor spreading since Late Oligocene time. Based on integrated analyses of seismic, well-logging and core data, we systematically document the sequence architecture and depositional evolution of the northern continental slope of the SCS and reveal its responses to tectonism, sea-level change and sediment supply. The infill of this shelf-margin basin can be divided into seven composite sequences (CS1-CS7) that are bounded by regional unconformities. Composite sequences CS3 to CS7 have formed since Late Oligocene time, and each of them generally reflects a regional transgressive-regressive cycle. These large cycles can be further divided into 20 sequences that are defined by local unconformities or transgressive-regressive boundaries. Depositional-geomorphological systems represented on the continental slope mainly include shelf-edge deltas, prodelta-slope fans, clinoforms of the shelf-margin slope, unidirectionally migrating slope channels, incised slope valleys, muddy slope fans, slope slump-debris-flow complexes and large-scale soft-sediment deformation of bedding. Changing sea levels, reflected by evidence from sequence architecture in the study area, are generally comparable with those of the Haq (1987) global sea level curve, whereas the regional transgressions and regressions were apparently controlled by tectonic uplift and subsidence. Composite sequences CS3 and CS4 formed from Late Oligocene to Middle Miocene time and represent continental-slope deposition during a time of northwest-northeast seafloor spreading and subsequent development of subbasins in the southwest-central SCS. The development of composite sequences CS5 to CS7 after Middle Miocene time was obviously influenced by the Dongsha Movement during convergence between the SCS and Philippine Sea plates. Climatic variations and monsoon intensification may have enhanced sediment supply during Late Oligocene-Early Miocene (25-21 Ma) and Late Pliocene-Pleistocene (3-0.8 Ma) times. This study indicates that shelf-edge delta and associated slope fan systems are the most important oil/gas-bearing reservoirs in the SCS continental-slope area.

Sedimentary evolution and controlling factors of Early-Mid Miocene Deltaic systems in the Northern Pearl River Mouth Basin, South China Sea

“…The dark mudstone with an abundant biodisturbed structure of FA6 represents the subaqueous tributary bay Figure 2. Sequence stratigraphy framework and depositional evolution of the Early-Mid Miocene in the northern Pearl River Mouth Basin (sequence divisions and fossil zones 19,[25][26][27] , tectonic and climatic events 28 ).…”

“…The argillaceous siltstone with horizontal bedding (FA5) is the distal delta front the deposits and can been interpreted as distal bar deposits. The bimodal cross bedding in the pelitic strip may be related to the scouring and backflow of the tides 26 , 29 , 30 . The dark mudstone with an abundant biodisturbed structure of FA6 represents the subaqueous tributary bay deposits.…”

Reassessing two contrasting Late Miocene-Holocene stratigraphic frameworks for the Pearl River Mouth Basin, northern South China Sea

“…Hence, the integration of seismic, lithological and biostratigraphic data allows not only a better recognition of stratigraphic boundaries, but also a better grasp of the regional geological history of a sedimentary basin when compared with using either method alone (Loutit et al, 1983;Van Wagoner et al, 1990;Haq, 1991;Catuneanu et al, 2009). High-resolution seismic and borehole data, together with detailed outcrop descriptions, have improved the practical frameworks for stratigraphic correlations adopted by industry and academia, providing important information on sedimentary processes acting in the deep-marine realm, and how these processes are controlled by regional tectonics, eustasy and rates of sediment supply (Johnson et al, 2001;Yoon et al, 2003;Miller et al, 2008;Flint et al, 2011;Lin et al, 2018;Patruno et al, 2018).…”

Clinoform growth and sediment flux into late Cenozoic Qiongdongnan shelf margin, South China Sea

“…Deepwater shelf margins or continental margin sedimentary prisms are important archives of clinoform architecture and evolving sedimentary regime during their construction (Chen, Steel, Olariu, & Li, ; Gomis‐Cartesio, Poyatos‐Moré, Hodgson, & Flint, ; Johannessen & Steel, ; Lin et al, ; Patruno & Helland‐Hansen, ; Ryan, Helland‐Hansen, Johannessen, & Steel, ). Specific aspects of margins have been highlighted such as (1) the geometry and sequence stratigraphy of individual high‐frequency clinothems (Lobo & Ridente, ; Pellegrini et al, ), the sand‐dominated (Carvajal, Steel, & Petter, ) vs. mud‐dominated (Poyatos‐Moré et al, ) character of the shelf break reaches of clinothems, (2) the relative effectiveness of storm waves, rivers, or tidal currents for dispersing sand onto the deepwater slope (Dixon, Steel, & Olariu, ), (3) the generation of sandy fan systems emplaced in clinothem bottomsets during rising and highstand of sea level (Carvajal & Steel, ; Covault, Normark, Romans, & Graham, ) and (4) forward numerical modelling of the topset width of shelf margin clinoforms (Burgess, Steel, & Granjeon, ).…”