关键词: 浅水湖盆, 河湖交互沉积, 浅水三角洲, 古地貌, 水位幕式升降, 河道, 花港组, 渐新统, 黄岩地区, 西湖凹陷, 东海陆架盆地

Abstract: Based on drilling core，well logging，and 3D seismic data，combined with evolution sequence recon-struction and spatial distribution depiction of depositional systems，the fluvio-lacustrine interactive depositional characteristics and sand-controlling mechanisms of Oligocene Huagang Formation in the shallow lacustrine basin of the Huangyan area，central-southern Xihu Sag of East China Sea shelf Basin were studied. The results show that：（1）There are three major depositional systems，including river-floodplain，shallow delta，and lacustrine systems，primarily developed from north to south in the Huagang Formation of the Xihu Sag. Huangyan area in central-southern region characterized by three sedimentary facies types：fluvial，shallow delta，and lacustrine. （2）The fluvial-lacustrine interaction system of the Huagang Formation in the Huangyan area can be subdivided into three distinct sedimentary units：river-dominated main area，fluvial-lacustrine transitional zone，and lake-dominated main area. The main area of the river control zone is developed with thick layers of gravel sandstone，and the seismic facies exhibit low-frequency weak amplitude characteristics；The interaction zone between rivers and lakes is characterized by the development of thick sandstone layers and an increase in mudstone interlayers. The seismic facies show low to medium frequency and weak amplitude，mainly consisting of implicit progradation and imbricate progradation；The mudstone in the main area of the lake is relatively developed，and the seismic facies are characterized by medium to high frequency and moderate to strong amplitude.（3）During the deposition of the Huagang Formation in the Huangyan area，micro-geomorphology and episodic fluctuations in water levels played pivotal roles. Within the isochronous framework of third-order sequences，three sand-controlling models for shallow lacustrine basins were established：During flood periods， the lake-dominated zone reached its maximum extent，with the main delta body submerged underwater and isolated sandbars developed.During average water levels，the lake level declined，the fluvio-lacustrine interactive zone expanded，resulting in laterally continuous sheet-like sandbodies and vertically separated sandbodies. During dry periods，the river-dominated zone predominated，with rivers shrinking into a network distribution and fine-grained sandstone deposition becoming more pronounced within channels.（4）The Huangyan area has developed multiple inverted anticline structures，with their limbs exhibiting significant potential for the development of large-scale structural-lithologic traps. favorable sand bodies are enriched in laterally superimposed lobes during flood periods，abandoned channels during normal flow periods ，and within channels during dry periods.

Key words: shallow-lake basin, river-lake interaction of sedimentation system, shallow water delta, paleogeo-morphy, curtain rise and fall channel of water level, channel, Huagang Formation, Oligocene, Huangyan area, Xihu Sag, East China Sea shelf Basin