准噶尔盆地东部隆起石钱滩凹陷石钱滩组层序划分

Sequence Division of Shiqiantan Formation in Shiqiantan Sag on Eastern Uplift of Junggar Basin

为建立石钱滩凹陷上石炭统石钱滩组标准剖面,给凹陷内井下地层划分对比及油气勘探提供依据,以野外调查为重点,利用地质探槽,根据岩性特征、沉积建造、接触关系、标志层、生物化石等综合分析,进行石钱滩组层序划分和沉积相恢复及区域地层对比。石钱滩组由洪积扇(扇三角洲)沉积开始,经扇前湖泊沉积,于海湾潟湖沉积结束,构成3次海侵退积型层序,可划分为3段。下段下部为砾岩和砂砾岩,夹砂岩和粉砂岩,中部为中—细砾岩、杂砂岩与泥岩和粉砂质泥岩互层,上部为粉砂质泥岩、泥岩夹砂岩和粉砂岩;中段下部为砾岩、含砾砂岩和砂岩,夹粉砂岩,上部为钙质粉砂质泥岩、泥岩、粉砂岩和泥质灰岩;上段下部为砾岩、砂岩与粉砂岩和粉砂质泥岩互层,中部为紫褐色、砖红色泥岩和泥质粉砂岩,夹含砾粗砂岩和砾岩,上部为深灰色泥岩和粉砂质泥岩夹灰岩。宏观上为下段、中段及上段上部为深灰色,上段下部为浅褐—砖红色,各段均为正粒序。扇前沼泽—海湾潟湖相暗色泥岩为有利烃源岩,扇中、扇端砂岩和砾岩为储集层,生储配置好,油气地质条件优越。

In order to establish a standard section of the Upper Carboniferous Shiqiantan formation in the Shiqiantan sag on the eastern up-lift of the Junggar basin,and to provide a basis for the division and correlation of the subsurface strata and for the oil and gas exploration in the sag,field survey was carried out.By using geological coastean,and through comprehensive analysis on lithological characteristics,sedi-mentary formations,contact relationships,marker beds,and paleontological fossils,the sequence division,sedimentary facies restoration,and regional stratigraphic correlation were completed for the Shiqiantan formation.The Shiqiantan formation underwent the deposition of al-luvial fan(fan delta),pre-fan lake and bay lagoon,forming three transgression-retrogradation sequences.The Shiqiantan formation can be divided into three members.The lower member is composed of conglomerate and sandy conglomerate intercalated with sandstone and silt-stone in the lower part,medium-fine grained conglomerate,graywacke,and interbeds of mudstone and silty mudstone in the middle part,and silty mudstone and mudstone intercalated with sandstone and siltstone in the upper part.The middle member is composed of conglom-erate,pebbly sandstone and sandstone intercalated with siltstone in the lower part,and calcareous silty mudstone,mudstone,siltstone and argillaceous limestone in the upper part.The upper member is composed of conglomerate,sandstone and interbeds of siltstone and silty mudstone in the lower part,purple-brown and brick-red mudstone and argillaceous siltstone intercalated with gravel-bearing gritstone and conglomerate in the middle part,and dark grey mudstone and silty mudstone intercalated with limestone in the upper part.Macroscopically,the lower member,middle member,and the upper part of the upper member are dark grey,and the lower part of the upper member is light brown to brick-red;all members are normally graded.The dark mudstones of pre-fan swamp-bay lagoon facies are favorable source rocks,while the sandstones and conglomerates of mid-fan and fan-apex facies are reservoir rocks.The good source-reservoir assemblage suggests favorable petroleum geology conditions.