Holocene evolution of the Qiongzhou Strait between Hainan Island and mainland China: Evidence from geological drilling

The Qiongzhou Strait, situated between Hainan Island and mainland China, has experienced a complex late Cenozoic evolution involving successive phases of marine flooding and land bridge exposure. Its last Holocene phase of evolution is important for understanding regional tectonics, climate dynamics, and ancient human migration patterns. In this paper, we integrate drilling data, microfossil analysis, and AMS ¹⁴C dating, to show that coastal sedimentation established on both sides of the strait at ∼11.2 ka BP, and full east-to-west seawater flooding occurred at ∼9.0 ka BP. The strait's evolution comprised six phases: (1) A land bridge existed before ∼12.0 ka BP; (2) Seawater inundation of low-lying areas occurred at ∼12.0–11.2 ka BP; (3) Rapid sea-level rise and complete strait opening occurred during ∼11.2–9.0 ka BP; (4) Fluctuating sea-level rise, peaking 2–3 m above current levels and resulting in maximum strait width, occurred at ∼9.0–6.0 ka BP; (5) Sea-level regression and marine plain exposure occurred ∼6.0–1.0 ka BP; (6) Stabilized coastlines developed after ∼1.0 ka BP. These stages highlight the interplay between postglacial sea-level changes and regional tectonic subsidence, providing a framework for reconstructing paleoenvironmental shifts in the northern margin of the South China Sea. The development of full marine connection at ∼9.0 ka BP underscores the long-term importance of the strait's role as a hydrographic corridor through the Holocene.