Sedimentological, paleontological, and mineralogical data from core XK-1 in the Xisha Islands allow for a detailed lithologic and sequence stratigraphical analysis on the Late Oligocene interval in the Xisha Islands. In this study, 13 facies are differentiated and a depositional model of a carbonate-dominated system is established. Variation in facies stacking patterns, changes in composition and grain size, and fluctuation in abundance of terrigenous matter are analyzed, and sequence division is interpreted at two different hierarchal levels. In the Late Oligocene interval of core XK-1, a total of thirteen small-scale sequences and three medium-scale sequences are divided out, with one medium-scale sequence mainly composed of four small-scale sequences. Based on the available timing constraints, the durations of the small- and medium-scale sequences are estimated to be 100 kyr and 400 kyr, respectively. These small-scale and medium-scale sequences are thus inferred to be primarily controlled by orbital forcing. The long-term evolution between 24.3 and 23.6 Ma was controlled by the eustatic sea level, while it was more influenced by a tectonic subsidence linked to the ridge jump event in the South China Sea after 23.6 Ma. Our study demonstrates that eustatic sea level fluctuations had a significant impact on the initial carbonate development at various scales in the northern South China Sea, while tectonic movement also played an important role in shaping the secular carbonate evolution.

来自西沙群岛XK-1岩心的沉积学，古生物学和矿物学数据可以对西沙群岛晚渐新世间隔进行详细的岩性和层序地层分析。在这项研究中，区分了13个相，并建立了以碳酸盐为主的系统的沉积模型。分析了相堆积模式的变化，成分和晶粒大小的变化以及陆源物质的丰度波动，并在两个不同的层次上解释了序列划分。在核心XK-1的晚渐新世间隔中，总共划分了13个小规模序列和3个中等规模序列，其中一个中等规模序列主要由4个小规模序列组成。根据可用的时间限制，中小规模序列的持续时间分别估计为100 kyr和400 kyr。因此，推断这些小规模和中等规模的序列主要受到轨道强迫的控制。24.3和23.6 Ma之间的长期演化受海平面的控制，而受23.6 Ma之后南海山脊跳跃事件相关的构造沉降的影响更大。我们的研究表明，在南海北部，不同水平的海平面波动对海床的初始碳酸盐发育有重要影响，而构造运动在塑造长期碳酸盐演化中也起着重要作用。因此，推断这些小规模和中等规模的序列主要受到轨道强迫的控制。24.3和23.6 Ma之间的长期演化受海平面的控制，而受23.6 Ma之后南海山脊跳跃事件相关的构造沉降的影响更大。我们的研究表明，在南海北部，不同水平的海平面波动对海床的初始碳酸盐发育有重要影响，而构造运动在塑造长期碳酸盐演化中也起着重要作用。因此，推断这些小规模和中等规模的序列主要受到轨道强迫的控制。24.3和23.6 Ma之间的长期演化受海平面的控制，而受23.6 Ma之后南海山脊跳跃事件相关的构造沉降的影响更大。我们的研究表明，在南海北部，不同水平的海平面波动对海床的初始碳酸盐发育有重要影响，而构造运动在塑造长期碳酸盐演化中也起着重要作用。