摘要:
江苏句容地区的上石炭统船山组碳酸盐沉积发育泥晶灰岩、细晶灰岩、生物碎屑泥晶灰岩、泥晶生物碎屑灰岩、含生物碎屑泥晶灰岩和含生物屑核形石灰岩6种岩性,可区分出潮坪、开阔台地、台盆、浅滩和生物礁5种相类型.这套碳酸盐沉积序列由S1、S2和S3三个层序构成,其中S1为Ⅰ型层序,S2和S3为Ⅱ型层序.依据岩性、沉积相、古生物与元素地球化学特征编制出的相对海平面变化曲线,反映船山组经历了3次海平面相对上升和下降.相对海平面升降控制了层序的发育,层序S1由滨海砾岩-潮坪结晶灰岩(低水位体系域)、台盆相含生物碎屑泥晶灰岩-泥晶灰岩(海侵体系域)和浅滩相含生物屑核形石灰岩(高水位体系域)构成;层序S2由生物礁相泥晶生物碎屑灰岩与开阔台地相生物碎屑泥晶灰岩-含生物碎屑泥晶灰岩-泥晶灰岩(海侵体系域)和开阔台地相含生物碎屑泥晶灰岩(高水位体系域)构成;层序S3由开阔台地相泥晶灰岩(海侵体系域)和浅滩相含生物屑核形石灰岩-潮坪相结晶灰岩-块状灰岩(高水位体系域)构成.下扬子区船山组是在构造相对稳定背景下发育的一套以开阔台地为主局部有滩有盆出现的碳酸盐沉积.开阔台地和台盆环境中沉积的灰岩是良好的生油层位,礁滩环境中的灰岩具备良好的储集性能.%The carbonate rocks of the Upper Carboniferous Chuanshan Formation in the Jurong area consist mainly of cryptite,fine crystalline limestone,bioclastic cryptite,micrite bioclastic limestone,clastizoic cryptite and clastizoic oncolite limestone,in which several platform carbonate depositional facies,including tidal flat,open platform,platformal trough,shoal-reef and organic reef,can be identified.The carbonate succession of the Chuanshan Formation is composed of three third-order deposition sequences:Type-Ⅰ sequence S1,and Type-Ⅱ sequences S2 and S3.Based on lithology,sedimentary facies,paleontology and geochemistry characteristics,the relative sea-level change curve was established,indicating there were three relative sea-level changes during the evolution of the Chuanshan Formation.These relative sea level changes controlled the development of sequences.S1 comprises the lowstand systems tract (LST) of conglomerate of shore limestone and crystalline limestone of tidal flat,transgressive systems tract (TST) of clastizoic cryptite and cryptite developed in platformal trough,and highstand systems tract (HST) of clastizoic oncolite limestone developed in shoal.S2 is made of TST of micrite bioclastic limestone in reef,bioclastic cryptite,clastizoic cryptite and cryptite in open platform,and HST of clastizoic cryptite in open platform.S3 composes TST of cryptite in open platform,HST of clastizoic oncolite limestone in shoal,and crystalline and clumpy limestones in tidal flat.In general,the carbonate platform of the Chuanshan Formation in the Lower Yangtze region developed in a shallow environment with relatively stable tectonic background;there also existed shoal and trough in the platform.Limestones in the open platform and platformal trough are high-quality source rocks while shoal reef limestones are good reservoir rocks.