南海北部洋陆过渡带的重力流沉积

The proposal attempts to investigate the types, sedimentary characteristics, tempo-spatial distribution, and formation mechanisms of various gravity-flow deposits (including turbidites, debrites, and submarine-landslide deposits) in the drilling area of IODP Expedition 367/368 at the northern continent-ocean transition of the South China Sea. By doing so, core, geophysical well-logging and seismic data will be integrated. The types and sedimentary characteristics of the gravity-flow deposits will be analyzed by various core sedimentological approaches, including core observations, core X-ray photographs, and thin-section, grain size and mineral composition analyses, as well as core measurements of associated physical and geochemical properties like magnetic susceptibility, density, lightness, and total organic carbon. Well-log facies analysis, calibrated by core data, will be used to detect the distribution of the gravity-flow deposits in the intervals with low core recovery or non-coring. Seismic stratigraphic analysis, tied to well control and constrained by geological age model, will provide a time-stratigraphic correlation framework for investigating the lateral distribution of the gravity-flow deposits and for evaluating the synchroneity of the various gravity-flow events. Flow behaviors of paleo-gravity flows will be quantitatively evaluated by numerical modeling. Integration of core-based sedimentology, well-log facies analysis, seismic stratigraphy, and numerical modeling will provide insights into the formation mechanisms of the gravity-flow deposits and the potential linkages to crucial geological events including regional tectonics, topographic variations, climate and sea level changes, and sediment supply.

根据IODP 367/368航次钻探取得的岩心和测井资料，结合高分辨率多道地震数据，研究南海北部洋陆过渡带重力流沉积物的类型、特征、分布及形成机理，为理解南海深海沉积环境演变及油气、水合物资源勘探提供依据。通过岩心观察、岩心X光照相、高密度取样分析（薄片、粒度、矿物成分等）及岩心物性和地化测试（磁化率、颜色反射率、有机碳等），研究重力流沉积物的类型及沉积特征；在岩心标定基础上，根据测井相分析预测未取心或低取心率井段重力流沉积的类型及分布；通过地震地层分析，结合年龄模式，建立区域等时层序地层对比格架，研究井间重力流沉积的横向分布及重力流事件的等时性；通过数值模拟估算重力流的流动参数（流速、浓度及流体厚度等）；综合岩心沉积学、测井相、地震地层与数值模拟研究，探讨重力流沉积的形成机理及其与区域构造、海底地形地貌演变、气候、海平面变化、物源供应等重要地质事件之间的成因联系。

本项目根据IODP367/368航次在南海北部洋陆过渡带获得的钻探资料，通过岩心观察、薄片（涂片）鉴定、粒度分析及岩石物性资料分析，结合反射地震和海底多波束测深数据解释，研究南海北部洋陆过渡带重力流沉积物的成因类型、沉积特征、时空分布及控制因素。鉴别出了三种成因的重力流沉积类型，分别为浊流沉积、碎屑流沉积和滑塌堆积，以浊流沉积为主。根据颗粒组成，进一步将浊流沉积划分为陆源碎屑、钙质和陆源碎屑-钙质混合沉积三类。三类浊积岩中，陆源碎屑浊积岩的丰度最高，然后依次为混积和钙质浊积岩。南海北部洋陆过渡带重力流沉积的形成始于早中新世，但大量发育始于晚中新世，重力流沉积最为发育的两个时段分别是晚中新世和中-晚更新世。晚中新世以来，钙屑浊积岩的丰度急剧减少。南海北部下陆坡到深海平原过渡部位发育大量超临界浊流有关的侵蚀-沉积地貌及底形。珠江海底峡谷以西的一统暗沙海底峡谷到海底扇裙过渡部位，超临界浊流底形的发育始于晚中新世，主要有两种底形组合，分别是冲坑、水跃坝及叠加在水跃坝上的逆行沙丘底形组合和阶梯状的周期阶坎底形组合。珠江海底峡谷以东，源自下陆坡北东向海山之间沟谷及从马尼拉海沟西侧溢出的浊流在陆坡-深海平原过渡部位形成了面积达24000km2的巨型沉积物波区，沉积波的发育时代为第四纪，组成沉积物波的底形类型顺坡而下从周期阶坎，依次递变为逆行沙丘和顺坡迁移底形。南海北部洋陆过渡带重力流沉积的发育与南海北部大陆边缘进入裂后热构造沉降阶段、被动大陆边缘逐渐发育成熟，扩张期后洋壳冷却、海盆水深逐渐增大，南海碳酸盐产率逐渐下降，全球海平面变化，以及与区域或局部构造活动（特别是第四纪台湾快速隆升）有关的物源供应变化等因素有关。