南海西北部琼东南盆地陆架坡折带类型及沉积作用特征

陆架坡折带特殊的地形地貌反映了其独特的水动力和沉积特征。根据水深和高分辨率单道地震资料对琼东南盆地陆架坡折带特征进行分析,旨在探讨现代陆架坡折带的成因及其沉积作用。研究结果表明,琼东南现代陆架坡折带呈NE-SW向展布,水深变化大,形态复杂,自西向东陆架坡折差异较大。西部陆架坡折带水深范围为250~700 m,宽约7 km,高差450 m,坡度平均为2°,地形平缓,槽谷不发育;中部陆架坡折带水深范围为250~750 m,宽约10 km,高差500 m,地形平均坡度为7°,槽谷呈V型或U型,长约5~6 km,宽约3~8 km,下切深度100~300 m;东部陆架坡折带水深范围为400~1 500 m,宽约30 km,高差达1 100 m,平均坡度为10°,槽谷呈"V"型,长约13~28 km,宽约为3~4 km,下切深度最大达500 m。结合琼东南盆地构造区划和物源特征,对琼东南陆架坡折带沉积作用进行分析,划分坡折带类型。西部陆架坡折带以大量的沉积物不断加积为主,地形平缓,槽谷不发育,属堆积型陆架坡折;中部属过渡型陆架坡折带,沉积物供应量小,侵蚀和堆积作用同时存在,相互制约,槽谷规模小,滑塌作用较弱;东部为侵蚀型陆架坡折,以底流冲刷侵蚀为主,槽谷及滑塌发育。总体反映了不同区段位置沉积物供给,沉积物堆积,底流侵蚀等作用的差异,是形成现今陆架坡折地貌格局的重要因素。

CHARACTERISTICS OF SHELF BREAK AND SEDIMENTAION PROCESS AT THE QIONGDONGNAN BASIN,NORTHWESTERN SOUTH CHINA SEA

The shelf break zone has unique dynamic conditions and sedimentation processes. In order to reveal the origin of geomorphological features and related sedimentation, characteristics of the shelf break zone at the Qiongdongnan Basin are studied based on the bathymetry and high resolution single-channel seismic data. The results show that the water depth varies greatly in a complicated pattern along the SE-NW shelf break zone of the Qiongdongnan Basin. The west segment of the shelf break, where no gully is developed, is located at the water depth of 250 to 700 m. It is 500 m in depth, 7 km in width, with a mean slope of 2°. The middle segment of the shelf break, located at the water depth of 250 to 750 m, is 500 m in depth, 10 km in width, with a mean slope of 7°. U or V shape gullies are found at the middle segment and 5 to 6 km in length, 3 to 8 km in width, with an incision depth of 100 to 300 m. The east segment of the shelf break, located at the water depth of 400 to 1500 m, is 1100 m in water depth, 30 km in width, with a mean slope of 10°. There are many V shape gullies, which are 13 to 25 km in length, 3 to 4 km in width, with a maximum incision depth up to 500 m. The west segment of the shelf break zone is accumulative, whereas the east segment is erosional and the middle segment transitional. The results of this study could be used as the scientific base for the study of deep sea sedimentary process as well as oil and gas exploration in deep water areas.