Dominance of coralline algae in the South China Sea: Insights into their responses to paleoceanographic events over the last 20 million years

Abstract

The evolution of Earth's climate is primarily reconstructed from deep-sea cores, while data from shallow-water carbonate successions play only a supplementary role. Furthermore, most available information originates from Western Europe, with limited data from the Middle East and almost none from the Americas and the Far East. While there has been significant discussion on the response of coralline algae to sea-level changes, their reactions to other paleoceanographic events and the long-term trends in their composition, abundance, and richness remain poorly understood. This study examines coralline algae in the carbonate rocks of Well CK2 in the northern South China Sea. A total of twelve genera, eight families, and three orders of coralline algae were identified in 666 petrologic thin sections. Coralline algal abundance was relatively high, between 10 and 4.28 Ma. In the early Miocene, coralline algal richness exhibited three distinct increases at 17.55 Ma, 17.45 Ma, and 17.44 Ma, corresponding to the Miocene Climate Optimum, likely as a response to global warming during this period. The distribution of Mesophyllum declined in response to a series of cooling events over the past 20 million years. Between 14.13 and 8.77 Ma, the concentration of Aethesolithon corresponded to a long-term sea-level fall, while its extinction indicated a rapid sea-level rise. At 6.71 Ma, the increasing abundance of Lithothamnion aligned with a rapid sea-level rise. A relative sea-level fall at 10 Ma was recorded by an increase in shallow-water coralline algae, which may be linked to regional uplift caused by the Dongsha movement. The algal distribution in the Xisha Islands reflects major geological and climatic events over the past 20 million years, underscoring the value of coralline algae as indicators of past climatic and environmental changes. These findings provide a new perspective on the late Cenozoic carbonate systems of the Far East.