中文摘要：

南海北部沉积物成分在渐新世末（23．8Ma）发生剧烈改变，出现地球化学成分上的突变．并在深海沉积中发生沉积间断及滑塌堆积。这些沉积事件在时间上与南海扩张轴由东两方向转为北东-南西方向发生跳跃的时间十分吻合，是渐新世以来南海构造演化史上最为重大的构造事件。经过这次构造事件．白云凹陷由渐新世晚期的浅水陆架环境转为中新世以后的深水陆坡环境。南海北部地区沉积物源南渐新世近源为主转变为中新世远源为主的供给特点：并使南海北部地区自中新世以来总体呈现海侵的特征。这次沉积环境与物源突变事件对南海北部地区油气藏的形成影响深远。

英文摘要：

A significant change in composition of sediments of the northern South China Sea took place in the terminal Oligocene （23.8 Ma BP）, accompanied by an abrupt change in geochemical composition, and meanwhile there occurred a depositional hiatus and olistostromes in abyssal sediments. These sedimentary events coincided in time with the jump of direction of the seafloor spreading axis of the South China from E-W to NE-SW, representing the most important tectonic event in the tectonic evolution of the South China Sea since the Oligocene. Through this tectonic event, the sedimentary environment in the Baiyun subbasin was transformed from the neritic continental shelf in the late Oligocene to the continental slope since the early Miocene and the provenance of sediments in the northern South China changed from mainly proximal areas in the Ohgocene to mainly distal areas in the Miocene, and furthermore, the region has generally exhibited the feature of sea transgression since the early Miocene in the area. This abrupt change event has far-reaching influence on the formation of petroleum accumulations in the northern South China Sea.