杭洲湾地区晚第四纪下切河谷内部相结构与生物气勘探

本文根据杭州湾沿海平原大量的钻井、静力触探井和分析化验等资料，研究了下切河谷（钱塘江和太湖下切河谷）充填物的沉积建造和沉积相，以及浅层生物气藏分布特征。研究表明，末次冰期以来，随着海平面变化，杭州湾地区下切河谷演化经历了深切、快速充填和埋藏三个阶段。末次冰盛期，海平面下降的幅度大，增加了河流梯度、加强了下切作用，本区形成了钱塘江和太湖下切河谷，随后在冰后期被充填和埋藏，下切河谷的两侧为暴露地表的古河间地。根据岩石学、沉积结构和沉积构造特征，本区下切河谷充填沉积物表现为向上变细的沉积层序，可以划分为4个沉积相类型，有河床滞留沉积物到部分曲流河沉积体系的边滩沉积、河漫滩-河口湾沉积、河口湾-浅海沉积和河口湾沙坝沉积。在河漫滩-河口湾相沉积期间，由于海平面上升、潮流体系、沉积物供给和可容空间条件适合一个潮流沙脊体系的发育，该相中砂质透镜体可能代表下切河谷内发育的潮流沙脊。对于河口湾-浅海沉积和河口湾沙坝沉积而言，由于沉积条件不再有利，没有形成沙脊沉积。所有的商业性生物气都存储在下切河谷内河漫滩-河口湾砂质透镜体中。

Sedimentary facies of incised valley fillings of the Late Quaternary in Hangzhou Bay area and shallow biogenic gas exploration

Based on the analysis of a large number of drillings,the static sounding and chemical data obtained from the present Hangzhou Bay coastal plain,this paper presents the sedimentary facies and architectures of the Qiantangjiang River and Taihu incised valleys,and the characteristics of shallow gas reservoir distribution.Since the last glaciation,with variations in sea level,the development of incised valleys in the Hangzhou Bay area underwent three stages:1) deep-cutting stage;2) rapid-filling stage; and3) rapid-burial stage.The fall of global sea level during the last glacial maximum enhanced the fluvial gradient and river cutting,resulting in the formation of the large-scale Qiantangjiang River and Taihu incised valleys which were subsequently filled and rapidly buried in the post-glacial period,with the paleointerfluve being exposed to air on both flanks of the incised valleys.The sediments of the incised valleys show an upward-fining succession,and can be grouped into four sedimentary facies: gravel lag-deposit of in-channel to partly over bank sediments of a meandering river,flood plain-estuary,estuary-shallow marine,and estuary sand bar,based on lithology,paleontology,and sedimentary textures and structures.Because during the sedimentation of the flood plain-estuary facies,the conditions of sea level rising,tidal regime,sediment supply and accommodation space were suitable for the development of a tidal ridge system,the sand lenses associated with this facies may represent tidal ridge formation in the incised valley.For estuary-shallow marine and estuary sand bars,because the sedimentary conditions are no longer favourable,no sand ridge sediments were formed.All commercial biogenic gas is stored in the flood plain-estuary sand lenses of the incised valleys.