生物礁、滩、灰泥丘沉积特征及地震识别

Sedimentary characteristics of reef,shoal and limemud mound,and their seismic identification

通过对国内外典型的生物礁、滩及灰泥丘实例分析,寻求三者的识别方法,建立地震识别标志。依据生物礁、滩及灰泥丘沉积特征及其地球物理响应,提出"三角分类"方案,相应归纳出"点、线、面、体、时"综合地震识别法,其中"点"即分析单个地质体的地震反射结构和构型,"线"即分析地质体的沉积环境,"面"即刻画地质体的平面分布,"体"即刻画地质体的空间分布,"时"即解剖地质体的纵向旋回性。应用该方法在南海西北部深水区共识别出了5类生物礁、3类滩和2类灰泥丘。其中生物礁具有低频、中—强振幅、中连续反射结构,丘状反射构型,内部具有海侵—海退旋回,位于构造高部位,沉积于高能环境;滩呈低频、中连续、中—强振幅地震反射结构,席状地震反射构型,位于构造斜坡带,形成于高能环境;灰泥丘具有低频、强振幅、非连续反射结构,丘状地震反射构型,位于斜坡相对底部位,沉积于低能环境。"点、线、面、体、时"识别方法将沉积特征、环境能量、地球物理响应及旋回分析有机结合,能可靠地识别生物礁、滩及灰泥丘,揭示出南海西北部深水区局部发育生物礁,广泛发育碳酸盐滩。

Seismic identification marks are established by analyzing domestic and overseas cases of reef,lime-mud mound,and shoal.According to their sedimentary and geophysical characteristics,trigonometric classificationsis proposed.Accordingly,a new comprehensive recognition method,namedpoint,line,plane,volume and time,is adopted for identification of reef,lime-mud mound,and shoal.Pointrepresents seismic reflection configurations of single geologic body;linerepresents sedimentary environments;planecorresponds to plane distribution;volume corresponds to three-dimensional distribution; andtimerepresents longitudinal cyclicity.Using this method,we recognize totally five types of reefs,three types of carbonate mud mounds,and two kinds of shoals in South China Sea.Located at structure tops in high energy environment and controlled by transgression-regression cycles,reefs arecharacterized by low frequency,middle and high amplitude,moderately continuous mound reflections.Located at structure slopes in high energy environment,shoals are represented by low frequency,middle and high amplitude,moderately continuous mat reflections.Located at structure lower slopes in low energy environment,carbonate mud mounds are characterized by low frequency,high amplitude,discontinuous mound reflections.Application results show that our approach can effectively identify reef,lime-mud mound and shoal in the study area.