海底冲沟——深水沉积输运系统的“毛细血管”

Submarine Gullies:the Capillary of Deep-water Sediment Transport System

海底冲沟作为比海底峡谷、水道地貌尺度小1个数量级的微地貌,与海底峡谷、水道共同构成了完整的深水沉积输运系统。由于调查数据分辨率的限制,在前人研究中,海底冲沟的重要作用一直被忽视。海底冲沟是深水沉积输运系统的“毛细血管”,数量巨大,主要分布在大陆坡、岛礁边缘、河口冲积扇前缘、海底峡谷和水道内部,与深水工程安全、岛礁安全、深水沉积体系和深水油气储层预测息息相关。从识别特征、沉积环境、影响因素和形成机理等方面,系统介绍了海底冲沟的研究进展;从分布区域、坡度、形态和沉积特征等方面,探讨了海底冲沟与海底峡谷和水道之间的区别与联系,并给出了区分三者的方法。通过归纳不同沉积环境的海底冲沟特征,将其定义为:在坡度大于2°的地形中,重力流成因、直线型的微地貌尺度沟槽,具有宽度小、深度浅、长度短和形态笔直(弯曲度接近于1)的特点,其中,片状浊流成因的海底冲沟还具有相互平行和等间距分布的集群特征。

Submarine gullies belong to the submarine micro-geomorphology,which are smaller than the scale of submarine canyons and channels.Submarine gullies are less than 10 km long,less than 1 km wide,and less than 100 m deep.They form deep-water sediment-transport systems with submarine canyons and channels.Owing to the limitation of survey data resolution in previous studies,the important role of submarine gullies has been ignored in the evolution of the continental margin and the process of deep-water deposits.Submarine gullies are the"capillaries"of the deep-water sediment transport system occurring at dozens or even hundreds of times the sum of submarine canyons and channels.Moreover,submarine gullies are mainly distributed in the head of the deep-water sediment transport system,including continental slopes,island-and-reef margins,estuarine alluvial fan fronts,submarine canyons,and channel interiors.Submarine gullies are closely related to the safety of deep-water engineering and islands-and-reefs,process of deep-water deposits,and prediction of deep-water oil and gas reservoirs.The research progress of submarine gullies is introduced from the aspects of identification characteristics,sedimentary environment,influencing factors,and formation mechanisms.From the aspects of distribution area,slope gradients,shape,and sedimentary characteristics,the differences and relationships between submarine gullies,submarine canyons,and channels are discussed,and a method for distinguishing them is given.By summarizing the characteristics of submarine gullies around the world,submarine gullies are defined as linear grooves characterized by erosion or deposition caused by gravity flows in the steep seafloor(slope gradients>2°),which show the characteristics of submarine gullies as narrow,short,shallow,and straight(curvature≈1).Moreover,submarine gullies caused by sheet-like turbidity currents have group characteristics that are parallel to each other and equally spaced.