Cenozoic evolution of the Yangjiang-Yitong’ansha fault zone in the northern South China Sea: Evidence from 3D seismic data

Abstract

The Yanjiang-Yitong’ansha Fault Zone (YYFZ) traverses the Pearl River Mouth Basin (PRMB) and plays an essential role in basin formation and hydrocarbon accumulation in the PRMB. Because of the lack of seismic data, its distribution, evolution, and effect on the basin evolution in the Cenozoic are poorly known. Based on a detailed interpretation of 3D multi-channel seismic data and previous research results, the YYFZ was identified and characterized. It comprises a series of NW-trending strike-slip faults that exhibit horsetail and en echelon structures in the map view and flower-like or Y-shaped structures in the profile view. By comprehensively analyzing the Paleogene migration of depocenters, activity characteristics of the YYFZ-related faults, and the relationships between faults and sedimentary sequences along the YYFZ, we propose the sinistral motion of the YYFZ initiated at about 35 Ma. The YYFZ served as a transfer zone during the intense rifting in the PRMB from 65 to 35 Ma. Then due to the combined effect of the Indian-Eurasian collision to the west, the Pacific subduction to the east, and the proto-SCS slab-pull to the south, it became a sinistral transtensional fault from 35 Ma to 16.5 Ma. Our results highlight the significant role of the NW-trending fault systems in the basin formation and the regional tectonic evolution of the PRMB.

Formation Mechanism of NW-Trending Faults and Their Significance on Basin Evolution in Zhu III Depression of the Pearl River Mouth Basin, SE China

“…Meanwhile, the NW-trending sag-controlling faults formed in the rifting I period continued to be active, causing the southward migration of the depocenter. Moreover, during this stage, the long-axis direction of deposition shifted from ENE to WNW, which is a response the dextral transition of the regional stress field [21,27]. With the migration of the rifting and deposition, tectonic uplift took place in local areas.…”

“…The ENE-trending thrust faults cuts the WNW-trending thrust faults on the seismic reflection profile, indicating it formed at a relatively later stage and preserved more completely. The thrust faults trending in ENE and WNW have been also suggested to be widespread in the basement of the Zhu I and Zhu II depressions, based on the borehole-constrained high-quality 3D seismic data [18,19,27,60,61]. Additionally, it was also discovered that the boundary faults and some major normal faults within the Cenozoic basin cut through the Tg and converged with the pre-existing faults, similar to that in the Enping and Baiyun sags.…”

“…There is a basin-controlling fault zone trending NW in the east of the Zhu III Depression called the Yangjiang-Yitong fault zone. The northern segment of the fault zone separates the Zhu III and Zhu I depressions and was active from Mesozoic to Cenozoic, which has a great impact on the development of the Zhu III Depression [41,53], especially for the adjacent Yangjiang Sag [27,54]. Additionally, a NE-striking depression-controlling fault, known as the Zhu III South Fault, governed the formation of the Zhu III Depression as a half-graben, with faulting in the south and overlapping in the north.…”

“…It is thus clear that the NW-trending fault is very important for the evolution of the basin. However, there are still differing views on the formation mechanisms of NW-trending faults, including extension and strike-slip motion [25][26][27].…”