利用反射地震和多波束资料研究南海西北部麻坑的结构特征与成因

麻坑通常是由海底流体逸散形成的一种海底表面的残留地貌.本文所研究的区域主要位于南海的西北部，包括琼东南盆地的西南部和中建南盆地的中北部.该区域海底表面主要覆盖细粒沉积物，并且底流活动强烈，底流水道发育，为麻坑的形成和发育提供了有利条件.麻坑发育的主要因素是流体逸散系统，本文通过反射地震资料在本区发现了断层、气烟囱、泥火山、泥底辟、声空白/声混浊、强反射等多种与流体逸散相关的指示特征.麻坑的几何特征随着区域的不同会有较大变化.首先本区麻坑的尺寸跨度较大，与底流水道伴生的麻坑和广乐隆起的麻坑表面宽度通常是几十米到数百米，其他区域麻坑的表面宽度通常可达数千米，被称为巨型麻坑.其次本区麻坑的表面形态复杂多样，有圆形、椭圆形、新月形、环形等.各种不同的形态有可能指示了麻坑的不同发育阶段，新月形麻坑可能发育程度较低，其次是环形，圆形则相对较为成熟.据此推断发育程度较低的新月形麻坑有可能是活动麻坑，而地震海洋学的资料也倾向于证实这一点.

Structural characteristics and genesis of pockmarks in the northwest of the South China Sea derived from reflective seismic and multibeam data

Pockmarks are usually residual topographies caused by fluids escaping through the seafloor. The study area of this paper is located in the northwest of the South China Sea, including the southeast part of the Qiongdongnan basin and the north-central part of the Zhongjiannan basin. The fine-grained sediments of the seabed as well as the strong bottom current provide favorable conditions for the formation and development of pockmarks. The main factor for the development of pockmarks is the fluid flow system which is related with faults, gas chimneys, mud volcanoes, mud diapirs, acoustic blanks/acoustic turbidities and enhanced reflections in the study area. The geometric features of pockmarks vary in different regions. Firstly, the sizes of pockmarks change greatly, with widths of tens to hundreds of meters for those associated with bottom current channels and those in the Guangle uplift, and thousands of meters for other portions in the study area, which are usually called giant pockmarks. Secondly, the surface morphologies of pockmarks are complicated, including circle, ellipse, crescent and annulus, which may indicate different stages of pockmark development. Crescent pockmarks may be younger, followed by annular pockmarks, and the circular ones are relatively older. According to this point, the crescent pockmarks are possibly active, which seems to be supported by data of seismic oceanography.