Tectonic affinity between the southern East China Sea Basin and the northern South China Sea margin

This study investigates the tectonic connection between the southern East China Sea Basin (ECSB) and the opening of the South China Sea (SCS). By integrating sedimentary records, seismic stratigraphy, and detrital zircon geochronological evidence, we propose that the tectono‑sedimentary evolution of the southern ECSB is closely linked to the opening and subsequent contraction of the SCS.

During the Paleocene‒Eocene, the southern ECSB (represented by the Lishui‒Jiaojiang Sag) and the basins around Taiwan exhibited highly similar evolutionary features: synchronous marine transgression, extensive paralic to shallow‑marine deposition, and diffuse extension lacking distinct boundary faults. This pattern contrasts sharply with the narrow, fault‑controlled half‑grabens in the northern ECSB. A key piece of evidence is the development of a major breakup unconformity in both regions during the late Eocene‒early Oligocene. This unconformity is characterized by truncation and tilting without compressional structures and corresponds in time to the initial opening of the SCS.

Detrital zircon U‒Pb dating provides independent support for the tectonic correlation between the two regions. Late Eocene sediments in the southern ECSB display a distinct provenance signature, with age spectra highly consistent with those of the northeast Mindoro block on the southern SCS margin, indicating that both belonged to the same continental block prior to breakup. Furthermore, the subsequent subduction and contraction of the SCS oceanic crust beneath the Philippine Sea Plate has brought the present‑day southern East China Sea into a subduction‑related tectonic setting.

Based on the synchronicity of sedimentary‑tectonic evolution and provenance links, combined with previous reconstructions of subducted slabs, we propose that before the opening of the SCS, its northern passive margin extended eastward, encompassing the southern ECSB. The Paleogene extension, sedimentary infill, development of the breakup unconformity, and subsequent tectonic processes in the southern ECSB were thus predominantly controlled by the rifting/spreading and eventual consumption of the eastern SCS. This understanding provides a new perspective for deciphering the tectonic connectivity of the East Asian continental margin.