Sedimentological, paleontological, and geochemical data from core XK-1 on the Xisha Islands have allowed for a detailed documentation of the early carbonate development around the Oligocene-Miocene transition in the northern South China Sea (SCS). The deposits within the fore reef, reef, lagoon environments occurred before 23 Ma, the exposure horizon occurred around 23 Ma, and the sediments within the open lagoon setting dominated after 23 Ma. This evolution indicates a sedimentological response to water depth change, which is the combined result of eustatic sea-level fluctuations and tectonic subsidence. The tectonic subsidence during the latest Oligocene and Early Miocene (especially this period) was responsible for the obvious deepening trend. What's more, substantial physical erosion caused an increased amount of terrigenous input into the Xisha Islands area, with detrimental effects on carbonate development after the Oligocene-Miocene boundary. Over the entire South China Sea, the early carbonate systems along the northern and southern margins displayed specific evolution patterns. After comparing these patterns, we found a close relationship between the carbonate initiation and the subduction of the proto-SCS and the opening of the modern SCS. Therefore, it has been demonstrated that sea level and local tectonics as well as paleoclimatic conditions were the main controlling factors in shaping the onset of carbonate sedimentation in the SCS.

来自西沙群岛 XK-1 岩芯的沉积学、古生物学和地球化学数据，可以详细记录南海北部 (SCS) 渐新世-中新世过渡期早期碳酸盐岩的发育。前礁、礁、泻湖环境中的沉积物发生在 23 Ma 之前，暴露层位发生在 23 Ma 左右，23 Ma 之后开放泻湖环境中的沉积物占主导地位。这种演变表明对水深变化的沉积学响应，这是海平面波动和构造沉降的综合结果。晚渐新世和早中新世（特别是这一时期）的构造沉降是明显的加深趋势。更重要的是，大量的物理侵蚀导致西沙群岛地区陆源输入量增加，对渐新世-中新世界线后碳酸盐岩的发育产生不利影响。在整个南海，南北边缘的早期碳酸盐岩系统呈现出特定的演化模式。通过比较这些模式，我们发现碳酸盐的形成与原始南海的俯冲和现代南海的开放之间存在密切的关系。因此，已经证明海平面和局部构造以及古气候条件是形成南海碳酸盐沉积开始的主要控制因素。北部和南部边缘的早期碳酸盐岩系统显示出特定的演化模式。通过比较这些模式，我们发现碳酸盐的形成与原始南海的俯冲和现代南海的开放之间存在密切的关系。因此，已经证明海平面和局部构造以及古气候条件是形成南海碳酸盐沉积开始的主要控制因素。北部和南部边缘的早期碳酸盐岩系统显示出特定的演化模式。通过比较这些模式，我们发现碳酸盐的形成与原始南海的俯冲和现代南海的开放之间存在密切的关系。因此，已经证明海平面和局部构造以及古气候条件是形成南海碳酸盐沉积开始的主要控制因素。