<p>The Zhujiang River Mouth Basin, a primary depocenter for terrigenous sediments in the western Pacific, presents a semienclosed tectonic setting with limited exchange with the open ocean. This unique feature enables systematic linkages among sedimentary processes, climate change, regional sea-level fluctuations, and tectonic events. To explore these linkages, this study focuses on Well PY35 in the Baiyun Sag of the Zhujiang River Mouth Basin. By integrating microfossil analysis with Milankovitch cycle analysis of well log data, an astronomical time scale (ATS) (17.54–7.80 Ma) and a high-resolution stratigraphic framework were established, allowing for the calculation of sedimentation rates across different hierarchical sequences and time intervals. The results indicate that between 17.54 Ma and 7.80 Ma, the sedimentation rate initially increased and then decreased, ranging from 6.1 cm/ka to 45.7 cm/ka, with an average rate of 22.2 cm/ka. During the Middle Miocene Climatic Optimum (MMCO), sedimentation rates were moderate and exhibited an increasing trend, largely driven by increased sediment input due to enhanced weathering from rising temperatures and by expanded accommodation space resulting from tectonic subsidence. Meanwhile, the Middle Miocene Climate Transition (MMCT) was marked by a notable rise in sedimentation rates, consistent with a major sea-level fall due to global cooling, which promoted the direct seaward progradation of marginal sediments. The Late Middle Miocene to Late Miocene had the lowest sedimentation rates, which can be attributed to reduced weathering under cold and arid conditions, along with a sea-level rise induced by regional tectonics. The short-term increase in the sedimentation rate observed at 10.4 Ma may have been driven by sea-level fluctuations. This study provides both theoretical and empirical support for understanding the influence of abrupt climate changes on sedimentary processes.</p>