西湖凹陷春晓区带下第三系平湖组、花港组沉积特征

SEDIMENTARY CHARACTERISTICS OF EOGENE PINGHU FORMATION AND HUAGANG FORMATION IN CHUNXIAO ZONE OF XIHU LAKE DEPRESSION

西湖凹陷春晓区带下第三系平湖组及花港组可划分出半封闭海湾、湖泊、三角洲及河流 4种主要的沉积体系类型 ,以及滨岸潮坪、泻湖、滨岸湖泊、河控三角洲、潮控三角洲、河流等 6种主要的沉积相类型和若干种亚相及微相。平湖组、花港组的发育与演化显示了由海到陆的变化特点 ,即平湖组主要为半闭塞海湾环境 ,以海湾泻湖相发育为其特征。花港组则以湖泊、三角洲、河流体系为主 ,并可明显两分 ,下段为海浸湖相 ,上段为淡水湖及曲流河泛滥平原的间互沉积。该区有利储集相带主要有潮渠水道、潮坪砂坝、河口坝、前缘席状砂及分流河道微相。

Eogene Pinghu Formation and Huagang Formation can be divided into four main sedimentary systems of semi-closed bay, lake, delta and river; and six main sedimentary types of shore-tidal flat , lagoon, shore-lake, river-controlling delta , tide-controlling delta and river etc., and several subfacies and microfacies. The development and evolution of the sedimentary systems in Pinghu Formation and Huagang Formation indicate change characteristics from the sea to the land; namely Pinghu Formation is chiefly composed of semi-closed bay environment with its own feature of development of bay-lagoon facies which is distributed largely in the central belt of working area. Huagang Formation consists mainly \{sedimentary\} systems of lake, delta and river which apparently can be divided into two \{sedimentary\} systems; the lower section is made up of ingression lake facies, the upper section is composed of fresh \{water\} lake sediments and interlayering sediments of meandering river flooding plain. The lake sedimentary system is mainly distributed in the northeast and central part of the working area, the delta system is chiefly developed in the south and southeast part of the working area while the meandering river system developed in the west part. Tidal \{channel\}, tidal -flat bar, river mouth bar, front sheet-like sand and microfacies of braiding flow river are main \{favorable\} reservoir belts in the area.