基于沉积构型半定量化恢复古水深:以珠江口盆地白云凹陷为例

Semi-quantitative restoration of paleobathymetric of Baiyun Sag of Pearl River Mouth Basin based on depositional architecture

针对南海北部深水沉积盆地的古水深恢复这一难题,以珠江口盆地白云凹陷为例,根据陆架陆坡沉积特征,通过在三级层序格架内精细地震线描和层拉平恢复结合的沉积构型技术对白云凹陷裂后阶段5个关键地质时期(21 Ma、19.1 Ma、13.8 Ma、10 Ma和5.33 Ma)古水深进行研究。结果表明,21 Ma、19.1 Ma时期平均古水深<300 m,之后至13.8 Ma时期最大水深900 m。10 Ma和5.33 Ma时期,水深由1 100 m扩大至1 600 m。从21~5.33 Ma时期,陆架坡折带沿NW-SE向分布在白云北坡,古水深表现为西北陆架区浅,东南陆坡-深海平原区水体深。白云凹陷古水深整体上经历了浅海-半深海-深海的水体持续加深过程,存在2期(13.8 Ma和5.33 Ma)水深速率相对其他时期变快的时期,古水深变化速率分别为117和103 m/Ma,13.8 Ma时期水体加深速率最大。古水深的研究成果对白云凹陷热沉降史和沉积古地貌形态恢复具有重要研究意义。

Aiming at reconstruction of paleobathymetric depth in the deep-water sedimentary basins in the northern South China Sea, this paper takes the Baiyun Sag of the Pearl River Mouth Basin as an example. According to the sedimentary characteristics of the continental shelf and slope, this study is based on depositional architecture by characterization of seismic profile and bedding flattening in third-order sequence in five critical geological stages(21, 19.1, 13.8, 10 and 5.33 Ma) of post-rift stage in Baiyun Sag. The results show that the average paleobathymetric depth in the 21 Ma and 19.1 Ma stages is less than 300 m, from then to 13.8 Ma, the maximum paleobathymetric depth is 900 m. During the 10 Ma and 5.33 Ma stages, the paleobathymetric depth expanded from 1100 m to 1600 m. From 21 Ma to 5.33 Ma, the shelf break belt had spreaded along the northwest-southeast direction on the northern slope of Baiyun Sag. The paleobathymetric depth of northwest shelf area is shallow, and the southeast continental slope and deep sea plain area is deep on the plane. The paleobathymetric depth of the Baiyun Sag had undergone a continuous deepening process of shallow sea to semi-deep sea and finally deep sea, and there were two stages(13.8 Ma and 5.33 Ma) much faster paleobathymetric depth rate than other stage in Baiyun Sag,the paleo-water depth change rate is 117 m/Ma and 103 m/Ma respectively,and the deepening rate of the paleobathymetric depth was the largest in the 13.8 Ma stage. The result of paleobathymetric has important research and guiding significance for the determination of the key parameters of paleobathymetric for thermal depression history research and the restoration of sedimentary paleomorphology.