Paleogene Tectonic Evolution Controls on Sequence Stratigraphic Patterns in the Fushan Sag, Northern South China Sea

Abstract

Tectonism is of extreme importance to sequence stratigraphic patterns in continental sedimentary basins, affecting both the sequence architecture and interval makeup. Sequence stratigraphic framework of the Paleogene rifting succession in the Fushan Sag, Northern South China Sea, was built using 3-D and 2-D seismic data, complemented by drilling cores and well logs. One first-order and three second-order sequences were defined by basin-scale unconformities, and seven third-order sequences were identified on the basis of unconformities along basin margins and correlative conformities within the central basin. Analysis of palaeotectonic stress field, unconformities and subsidence history show that the Paleogene tectonic evolution presented significant characteristics of multistage and episode, and can be divided into three stages: rifting stage I (initial rifting period), rifting stage II (rapid subsidence period), rifting stage III (fault-depressed diversionary period). Partition of the west and east in tectonic activity was obvious. The west area showed relatively stronger tectonic activity than the east area, especially during the rifting stage II. Episodic rifting and lateral variation in tectonic activity brought into being a wide variety of structural slope break belts, which controlled different architectures and internal makeup of sequences, and strongly constrained the development of specific facies zones or sand bodies that tended to form hydrocarbon accumulation. This paper classified the genetic types of slope break belts and their relevant sequence stratigraphic patterns within the Fushan Sag, and further prospected the favorable sandstone reservoirs developing in particular tectonic positions and sequence stratigraphic patterns, which suggests that vertical evolution of structural slope break belts and relevant sequence stratigraphic patterns as a response to the Paleogene tectonic evolution were strongly controlled by sag margin types and spatial difference in tectonic activity. This not only enhances the understanding of tectonic evolution controls on sequence stratigraphic patterns, but also provided scientific evidence for petroleum exploration.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015