Sedimentary Evolution in the Northern Slope of the South China Sea Since the Oligocene and Its Response to Tectonics

Abstract

AbstractThe sedimentary evolution of the South China Sea (SCS) since the Oligocene and its response to tectonics was reconstructed based on a multi‐proxies approach including monomineralic quartz oxygen isotope ratios (δ18O), terrigenous grain‐size and accumulation rate, and scanning electron microscopy (SEM) observation of isolated quartz in sediments from Ocean Drilling Program (ODP) Site 1148 in the northern SCS. The sedimentary evolution of SCS could be divided into five stages: initial expansion (34~28.5 Ma), intense tectonic activity (28.5~23 Ma), reduced tectonic activity (23~16.5 Ma), thermal subsidence (16.5~3.5 Ma), and Taiwan uplift (3.5 Ma to present). Significant variations of the composition of terrigenous minerals and oxygen isotope values of quartz between 28.5 Ma and 23 Ma suggest a change in sediments provenance, which may be related to the strongest tectonic activity of the SCS in the Oligocene. Terrigenous materials at the study site were mainly originated from the southern source (presumptively from Palawan) during the early spreading period of the SCS. With the extensive spreading of the SCS, especially when the spreading axis of the SCS jumped southwards during 25~23 Ma, the Palawan continental block moved away from the study site. Moreover, the northern sources (South China) were not significant because of low topography at that time. Therefore, the terrigenous mass accumulation rate (MAR) was very low. Because of the rapid uplift of the Qinghai‐Tibet Plateau, Pearl River developed gradually and thus South China became the main source of ODP Site 1148. With the formation of the Taiwan island since 3.5 Ma, Taiwan contributed significant terrigenous materials to the northern SCS. The hiatus in sediments at ODP Site 1148 in the late Oligocene possibly resulted from the influence of low terrigenous materials supply, rising sea level and relatively stronger currents during provenance change.